The term mipenei darkhei shalom was the most commonly used term within Tannaitic literature, appearing in twelve mishnahs and toseftas. There is no one categorization of the way that mipenei darkhei shalom was used in Tannaitic literature. Below are the functions of the term that I found in both the Mishnah and Tosefta.
1. Where no clear legal conclusion or ruling already existed, mipenei darkhei shalom was used to justify a position that would promote better relations between groups of people within Jewish society or between Jews and non-Jews.
2. Where the question was not necessarily one of law, mipenei darkhei shalom was used to justify actions that would promote better relations between Jews and other Jews and between Jews and non-Jews.
3. In situations where there was a fear that the law was going to cause enmity, mipenei darkhei shalom was used to justify a lenient ruling whose purpose was to prevent enmity and ill-will from forming. In these instances, mipenei darkhei shalom was sometimes used to justify overturning a legal norm.
That these different functions were all found within Tannaitic literature is evidence that there was no single definition and understanding of how the term mipenei darkhei shalom should be used. It was used in a number of circumstances and the common thread through all of them was a concern for the effect that behavior based upon Jewish law might have on relations between different groups, whether they be within Jewish society, or between Jews and non-Jews.

Michael Pitkowsky, ”Mipenei Darkhei Shalom (Because of the Paths of Peace) and Related Terms: A Case Study of How Early Concepts and Terminology Developed From Tannaitic to Talmudic Literature” (PhD. diss., Jewish Theological Seminary, 2011), 169-170.