I am going out on a limb here, but I second Deer Hunter's position.
This was supposed to become a comment, but I write it as an answer ... Avoiding pointless comments on this answer, yes, I have read Robert's answer as well as Manishearth's answer.
Guys, have a look at high ranking questions and answers on Stack Overflow. What do you see? A hell of a lot of comments. And guess what, I read all of them if I am interested in the question/answer. It is pointless to dig for old chat logs (as long as you can not easily bidirectionally link chat protocols with questions/answers). It is useful to see e.g. how an answer came together and evolved based on comments. I learn by that. There is absolutely NO justification for 'cleaning them up'. Although people like to put things into clean categories i.e. answers or comments, the human mind just does not work like that. Please remember that.
Going out on a limb even more, moderating is a social discipline, is not it? It is not about the content and the subject as such. So if some of you (moderators) desperately want to 'clean up' anything here, may I suggest to call for e.g. special events on pre-announced dates in the chat? It could ensure that there are enough people around who understand the subject(s), enabling a subject-based review before stuff is deleted ... This site is for 'professionals' after all, or have I misunderstood something?
@Deer Hunter: subject domain-ignorant deletionism - it has happened before and it will happen again. It is just another strange side effect of group dynamics. At some point in virtually every system, the 'proper' maintenance of the 'nominal' as-is state becomes more important than real arguments, discussions or subject relevant content. It is not the internet, it is just peoples minds. In this context, a point- and badge-based system is not very helpful, either. All the luck to you, too.