My university (in France) is having a debate about the relevance of taking rules for preventing too many of its PhDs to be recruited here, or asking them to have some postdoc outside the region before. The same rules are also debated about the promotion to full professor (from what is called maître de conférence and is a tenured associate professorship).
Many people have strong opinion on these issues (me included), and I would like to gather a comprehensive list of arguments (in both directions) on this matter, if only to clear my ideas.
Some arguments may apply only under particular circumstances or in specific fields, please say so when it applies.