It has been suggested in [this question](https://softwareengineering.meta.stackexchange.com/questions/2225/what-is-an-extended-discussion/2227#2227) that comments should be for the purpose of clarification of a question or answer, and that eventually the clarifications should be editted into the question/answer so that people don't have to look down the comment change to see what was "really" meant. 

We took up a [policy of removing irrelevant comments](https://softwareengineering.meta.stackexchange.com/questions/1457/how-do-our-moderators-and-community-members-feel-about-cleaning-up-comment-nois), but it seems that the issue is larger now than just dealing with noise in comments.

When, if at all, should we delete comments? For that matter, is there any reason that comments should not just be deleted after a certain period of time? They can be fun to read, but do comments truly serve any purpose 6 months after they were posted if questions are being properly edited?