Our Gemara on Amud Beis discusses why a Talmid Chacham has special credibility; he never lies except for purposes of modesty and privacy. However, even a meticulously honest Torah sage is permitted to alter the truth under circumstances that would violate privacy or modesty, such as if he wants to modestly hide his wisdom, he may publicly deny his achievements. Additionally, he may use deception to prevent others from becoming aware of his and his wife’s intimacy. In general, the principle is that one may resort to untruth if it is to peace and well being (see Tosafos ibid, 24a, “Be-Ushpiza”.) Of course, such lies must not be self-serving and there must be no other reasonable way to promote peace and also must not cause future suffering or loss (see Shalah, Ner Mitzvah, Maseches Succah, 55 and Meiri Yevamos 63a.) In addition, it should not be in a situation where it will tend to become a habit (Yam Shel Shlomo, Yevamos 63.)
For example, if you come home late, it is not proper to lie and tell your wife you were on time, just to save your skin. But if a hostess burned the meatloaf one time, it is permitted to still compliment her.
There is also a ruling of the Magen Avrohom (OC 156, based on Sefer Chassidim 426 ) that one may only lie about past events, but not future ones. This is also in order to prevent forming a pattern of habitual lying. A lie about the past is almost always an ad hoc defensive action. But to lie about some future event or intention is a premeditated plan to deceive. This last point is debated by poskim, see Mishna Berura (ibid 4) who does not outright rule against the Magen Avraham and Sefer Casidim, but expresses that the ruling is difficult to understand. I have heard orally from some contemporary poskim that Sefer Chasidim’s standard is not the actual practice - check with your local Orthodox Rabbi for more guidance on the matter.
Ben Yehoyada notes that the Gemara uses the phrase “le-shanos -to alter”, as opposed to lying outright. This indicates that even when one is permitted to resort to deception, it should not be an outright lie, but rather a phrase that can be taken in different ways. (Also see Aroch Laner Yevamos 65b and Shemiras Halashon, Rechilus Kelal 1:8) Thus, going back to our meatloaf situation, do not say, “The meatloaf was delicious.” Instead say, “The meatloaf was exceptional.” She takes it to mean “exceptionally delicious”, but you mean “exceptionally awful”! Be’er Mayyim Chayyim (Bereishis 18:15) gives several biblical and Talmudic examples where a person needed to lie but was careful to use an expression that could, technically, be true. The most famous example is the Midrashic reconfiguration of Yaakov’s affirmation, “It is I, Esav, your firstborn” (Bereishis 27:19). But Rashi (ibid) also reads it as, “It is I, (Yaakov), who brought you this food. Esav, (however) is your firstborn.”
But what is the purpose of these word games? In the end, the words were chosen to mislead. If lying is permitted, so be it. Why does it matter what words you use?” If you eat treif with a shinuy (indirect manner), it’s still treif.
The simple answer is, as we saw from many examples above, extra care must be taken in regard to lying in order that it not become a habit. Therefore, we might say the idea of having the requirement to use awkward language, is to serve as a reminder that this cannot be a routine response.
Another idea that occurs to me is that, in Jewish thought, words are intrinsically sacred (see Bamidbar 30:3). Even though there is no debating that a series of words crafted with intention to mislead is just as forbidden as an outright lie, in terms of the prohibition to lie, it might be a separate distortion or contamination to corrupt the words. We see that words have power to create a reality, even to the extent that one should not idly make negative or pessimistic statements (Berachos 19a). Therefore, even when it is permitted to lie, there might be a separate prohibition against distorting the actual words. In his introduction to Emunos V’deos, Rav Saadiah Gaon speaks of the satisfaction and mental health that comes from being connected to truth, and psychologically speaking, habitually lying can lead to and reinforce harmful self-delusion.
The only thing I wonder about, is if using a phrase that is technically true, but actually fasle, can also lead to more rationalizations in the future, instead of calling a spade a spade. I would think it is more honest to oneself, to specifically not use any deceptive words in the circumstances which permit lying, so that there is no slippery slope effect. Perhaps the fact that the rabbis are not concerned with this, and instead focus on the actual damage of uttering a false word even in its literal sense, stems from the same sentiment that prompted the Gemara (Bava Basra 89b) to not be concerned that cheaters will learn certain legalisms from their Talmudic discussions:
Rabban Yoḥanan ben Zakkai said with regard to all these halachos about weights and measures: Woe to me if I say them, and woe unto me if I do not say them. If I say them, perhaps swindlers will learn new methods of cheating of which they were previously unaware. And if I do not say them, perhaps swindlers will say: Torah scholars are not well versed in our handiwork. A dilemma was raised before the Sages: Did Rabban Yoḥanan ben Zakkai decide to say these halakhos in public or did he not say them? Rav Shmuel bar Rav Yitzḥak says: He said them, and he said them on the basis of this verse: “For the ways of the Lord are right, and the just walk in them; but transgressors stumble over them” (Hosea 14:10).
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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