One of the most far-reaching disputes amongst the Tannaim (sages of the Mishnaic period) regarding the laws of Shabbos is regarding מלאכה שאינה צריכה לגופא ,literally a melacha done for a purpose other than the improvement of the object of the melacha, but usually understood by extension to refer to melacha done for a purpose other than the purpose it was done for in the work of the mishkan.
Unlike דבר שאין מתכוין, where there is no intention to perform the forbidden act at all, here the action is performed completely intentionally, but for a different purpose.
A classic example is where someone takes a dead body out of one’s domain on shabbos (Shabbos 93a)
This constitutes the forbidden melacha of הוצאה (“carrying” or transferring an item from one domain to another.)
However, in this case, the corpse in not removed because one wants it to be somewhere else, it is removed because one does NOT want it to be where it currently is.
In such a case, Rabbi Yehuda holds that he is biblically liable still, but Rabbi Shimon holds that one is exempt on a biblical level and has only transgressed a rabbinical prohibition.
Another classic example is someone who digs a hole in the ground (Shabbos 73b). This constitutes the melacha of חופר (ploughing), which is usually defined as making the ground more suitable for planting.
What happens, however, if a person digs a hole, not because he wants the resulting hole, but because he wants to make use of the dust or sand which he digs up?
According to Rabbi Yehuda, the purpose of the melacha makes no difference, so long as it is constructive, whereas according to Rabbi Shimon, although such an action is rabbinically forbidden, there is no biblical prohibition and one is thus exempt from the harsh biblical punishment associated with it. (note that when the hold is made inside one’s home, the Gemara opines that even Rabbi Yehuda exempts the person seeing as it is מקלקל. This seems to imply that if an action itself is destructive, even if it has a constructive purpose, one is still biblically exempt, which is rather problematic in light of the fact that some מלאכות such as making a wound, knocking down a building, or tearing are by definition destructive, but still biblically forbidden seeing as there main purpose is constructive. But this is for a different discussion (see Shabbos 31b regarding סותר על מנת לבנות במקום אחר for a possible approach)
It is generally understood (see Chagiga 10b where this is explicit) that this is another example of the exemption of מלאכת מחשבת, significant and calculated work – in this case the different purpose of the action reduces the significance or importance of the action , seeing as had it been done in the mishkan for such a purpose, it would not have been a significant part of the work performed there.

Another classic example of מלאכה שאינה צריכה לגופא is most cases of extinguishing a flame or a fire.
We should all be familiar with the famous Mishna said every shabbos evening )Shabbos 29b,) which records the view of Rabbi Yossi that one is only liable for extinguishing a flame if he does it for the wick itself, in order to make it easier to burn .
In contrast, extinguishing a fire simply because one wants it to be dark, or because one does not want to waste the oil or blacken the lamp, is only a rabbinical prohibition.
It is important to note that the תנא קמא (first opinion) in the same Mishna holds that one is biblically liable for such an action and is only exempt if it was done to prevent actual danger.
This aligns the view of the Tana Kama with that of Rabbi Yehuda, and Rabbi Yossi with Rabbi Shimon.
As it is a well known rule of psak, stated by the authoritative Amora Rabbi Yochanan, that the Halacha usually follows a סתם משנה (anonymous Mishna where no dissenting opinion is recorded,) finding such a Mishna which takes a stand on this subject could be a major factor in how we rule.
On this daf, we have at least 3 different examples of what appears to be מלאכה שאינה צריכה לגופא.
In the first Mishna on the daf, which is indeed a סתם משנה , we are told that it is forbidden to actively ask a non-Jew to extinguish a fire, but one does not have to stop him from doing so.
As the reason for the extinguishing the fire is clearly to save one’s property, and not for the wick, this seems to be a clear case of מלאכה שאינה צריכא לגופא.
If the author of our Mishna held that מלאכה שאינה צריכה לגופא is only a rabbinical prohibition, it seems rather harsh that he would forbidden asking a non- Jew to do this, giving the principle of שבות דשבות that we have discussed many times, which allows one to ask a non-Jew to perform a rabbinically forbidden melacha for the sake of a mitzva, great need, or distress.
There are very few greater needs than preventing one’s house from burning down chalila, and it would certainly be a severe form of distress if it did so.
One is forced to conclude that either the author of this Mishna holds that מלאכה שאינה צריכא לגופא is a biblical prohibition, or that he rejects the entire principle of שבות דשבות as stated.
Indeed, the Rambam, (Shabbos 1/7) rules like Rabbi Yehuda that מלאכה שאינה צריכה לגופא is a biblical transgression, and this Mishna might be one of his main sources for this.
In contrast, Rabbeinu Chananel, Raavad, Tosfos and many other authorities hold that מלאכה שאינה צריכה לגופא is only a rabbinical prohibition.
Accordingly, Tosfos on our daf states clearly that there is indeed no blanket permission for a שבות דשבות even for the sake of a mitzva or great need,(presumably he holds that the example we learn this leniency from in the gemara, namely bris milah, is an exception due to the fundamental uniqueness of this mitzva.)
Yet it is the view of many other authorities, as well as that of the Shulchan Aruch and Rema, that מלאכה שאינה צריכה לגופא is indeed only rabbinical, and that the leniency of שבות דשבות applies across the board, at least when the rabbinical action is performed by a non-Jew.
As such, in order to explain this Mishna, we would need to either

1. find another equally authoritative Mishna that holds that מלאכה שאינה צריכה לגופא is only rabbinical
2. Conclude that even according to Rabbi Shimon who holds that מלאכה שאינה צריכה לגופא is only rabbinical, it is more severe than most rabbinical prohibitions and the leniency of שבות דשבות does not apply to it.
3. Conclude that the author of our Mishna does not consider extinguishing a fire to save property to be מלאכה שאינה צריכא לגופא, in contrast to the explicit view of Rabbi Yossi who does.
4. Explain why Chazal where particularly strict in the case of our Mishna

In the next Mishna on the daf, we are told among other things that it is permitted to trap a scorpion on shabbos to prevent it from biting by covering it with a vessel.
However, the Mishna then states that such a case was brought in front of Rabban Yochanan ben Zakai and he expressed his concern that shabbos might have been desecrated unknowingly.
As it is obvious that if this was a poisonous scorpion that was likely to bite him, no one would argue that covering it was forbidden, it seems clear that we are talking about a non-toxic scorpion, and the basis of the Tana Kama’s leniency is that one does not want the scorpion, but merely to prevent it from damaging.
This makes it מלאכה שאינה צריכה לגופא, and given that it is only rabbinically prohibited in the first place, the Tana Kama permits it in order to prevent the pain inflict by a bite.
If this analysis is correct, we could be faced with another two Tannaim debating the status of מלאכה שאינה צריכא לגופא.

On the second side of the daf, the Amora (sage of the Talmudic period,) Rabbi Yehoshua ben Levi rules that any creature that causes damage may be killed on shabbos. Rav Yosef quotes a Beraisa that mentions 5 specifically dangerous creatures (one of them being the snake of Eretz Yisroel- probably the venomous Palestinian viper that is ironically a protected species despite the danger it poises to residents.)
He derives from this that other creatures that cause damage but are not life-threatening may not be killed on shabbos, which serves to disprove the lenient ruling of Rabbi Yehoshua ben Levi.
Rav Yosef reconciles these two statements by saying that everyone agrees that if a life-threatening creature is running towards him, poising an immediate danger, one may kill it.
In such a case, even Rabbi Yehuda agrees that it is permitted to kill them due to concerns for pikuach nefesh.
When it comes to other non-life-threatening creatures that nevertheless cause damage (such as biting,) Rabbi Yehuda would forbid it but Rabbi Shimon would permit it, seeing as it is מלאכה שאינה צריכה לגופא , which according to him is only rabbinically forbidden, and thus permitted to prevent damage. (see Rashi and Tosfos though for 2 different ways of understanding the Gemara’s answer.)
We have shown how 3 different cases on our daf form essential primary material in the analysis of the law regarding מלאכה שאינה צריכא לגופא, and its scope- the actual halacha is beyond the scope of this post, but familiar to any serious student of hilchos Shabbos.
In addition to its ramifications for this principle, this sugya seems to imply that although the golden rule with matters of pikuach nefesh is that ספק נפשות להקיל, in case of doubt, one always errs on the side of caution, this rule does have certain limits and the perceived danger to life does have to be more than just the realm of the paranoid.
This is further illustrated in the continuation of the sugya.
The Gemara tells how a Tana(in this context, reader of Beraitot, not someone from the tannaic period) taught a Beraita in front of Rabbah bar Rav Huna:
“One who kills snakes and scorpions on shabbos, the spirit of the Chasidim (pious ones) is not at peace with (does not approve.)”
Rabbah bar Rav Huna retorted that if this is the case, the spirit of the sages is not at peace with those Chasidim! (seeing as they were being stringent in the laws of shabbos at the expense of concern for safety!)
This reminds of the case of the חסיד שוטה, the foolish pious person, who sees a woman drowning and refuses to save her because it is not modest to look at her (Sotah 21b.)
Yet, for an entirely different reason, Rav Huna disagrees in this case.
The Gemara accounts how he once saw someone killing a wasp on shabbos, presumably for the above reason, and rebuked him, saying “Have you finished killing them all?”
Rav Huna seems to be of the view that given that there is no end to how many insects one can spend one’s shabbos killing, and the efficacy of each act in itself is doubtful, this is outside the normal concern of pikuach nefesh and in the realm of paranoia.
Once again, it is not our mandate here to come to halachik conclusions, but the basic messages of this incident need to be internalized – On the one hand, being concerned about other prohibitions at the expense of danger to life is considered “foolish piety” and not to be tolerated. On the other hand, we need to be able to distinguish between real, albeit small, concerns for life and actions with a reasonable chance of mitigating that risk, and obsessive paranoia with little efficacy.