This discussion is about establishing a general blanket policy about summarily removing comment threads that have been resolved and rendered no longer relevant.
I agree something needs to be done here, but I'm not comfortable with this if it goes beyond such clear cases like "please fix this typo".
It is too easy to misjudge the relevance of a comment thread, even if it seems resolved. Sometimes, to understand a question's edit history I need to see the comments as well. In other instances, a comment expresses a common misconception that then gets cleared up by the OP but is important for future generations so they don't repeat the same mistake.
Comment deletion is completely intransparent. There is no way to keep track of deleted comments, or protest their deletion. As long as this is the way it is, I don't think there should be a culture of deleting comments among mods, except for the generally accepted exceptions where it takes place already: When comments are rude, or a conversation gets completely derailed and off-topic.
Don't get me wrong: I think all our mods are highly competent individuals. But telling noise or obsolete comments from legitimate ones is tough, sometimes even for the people who actually participate in it! This should not be a moderator task.
I would be more comfortable with a system that enables the participants of a conversation to clean up whole threads in an easy way (I posted a suggestion here; I'm not saying it's perfect but something in this direction might work). People are aware of comments being noise, especially the more frequent users. But there is no good tool to remove noise at the moment - to me, looking into this would be the much preferable way.
[status-completed]tag or a blog post or something, so we have a reference to point to in the future!