The best practice guideline between settings.xml and pom.xml is that
configurations in settings.xml must be specific to the current user and
that pom.xml configurations are specific to the project.
For example, <repositories> in pom.xml would tell all users of
the project to use the <repositories> specified in the pom.xml.
However, some users may prefer to use a mirror instead, so they'll put
<mirrors> in their settings.xml so they can choose a faster
so there you go:
settings.xml -> user scope
pom.xml -> project scope