The overwhelming majority of redactional changes occurred in the discursive passages of the Talmud
…the overwhelming majority of redactional changes occurred in the discursive passages of the Talmud, the ones that contain arguments and discussions, rather than in the apodictic passages, the ones that contain fixed law. Apodictic passages apparently needed no improvement; they were not defective. Such a substantial difference could not have taken place accidentally. There must have been a conscious decision to preserve carefully the fixed law and to neglect benignly the argumentational material. After a conclusion was reached, the means of arriving at it, the arguments that went into making it, seemed no longer important. This should not surprise us; it is exactly the way the authors of the Mishnah and the Braitha (ca. 50-200 C.E.) practiced transmission.
David Weiss Halivni, Midrash, Mishnah, and Gemara: The Jewish Predilection for Justified Law (Cambridge, MA & London, UK: Harvard University Press, 1986), 2.