As a frequent user of Stack Overflow, I see a lot of conversations that happen in comments. Whole questions are answered in the comments. Often, the comments have useful information, but ultimately, the comments generate a lot of noise. Too much noise for even the most dedicated of users to keep up with.
No doubt, comments are useful at one point or another, but as time goes on, comments reach obsolescence. To date, we have not found a good way to handle this.
There are a few suppositions I'm making here (based on observation and lots of time moderating comments):
after a certain number of comments (say 10), it's hard to follow what's going on. Comments will often contain conversations between users interspersed with clarifications from the OP or the answerer interspersed with 'Thanks
Comments aren't moderated regularly by the people who post them. This is evident by the sheer number of comments that include clarification that is never edited into the question or the answer; or the number of times I've seen a user answer a question in a comment (I tried running SEDE queries for these to give you numbers, but it crashed Firefox each time).
There are orders of magnitude difference between the users that flag comments for moderation, and the users that police their own comments.
Lots of comments make the answers harder to follow, when the user has to scan through not only the answer, but its comments (and try to parse out the conversations from the relevant clarifications). This increases the friction for helping users find good answers.
Lots of comments make the questions harder to follow, for the same reasons. If the OP doesn't edit their question, but instead posts comments with code or with clarifications, a user has to parse all those comments to determine if the problem is the same as theirs.
This is only a problem for Stack Overflow, given we have over 111,127 posts that have more than 10 comments on them, and the next highest is Meta, with 5,936 posts with greater than 10 comments. Superuser jumps in at a paltry (by comparison) 2215.
How do we solve this? Remember, we only have a dozen or so moderators on Stack Overflow. If we now only have a few hundred users that flag comments, there's no way we could expect 12 moderators to do better than a few hundred users.
Is this even a problem? Should we even care about the number of comments? We know that comments are a necessary evil, but are we harming ourselves by allowing the number of comments to proliferate at an exponential rate, and never having an efficient means to prune them?
Why should comments be a necessary evil? Is there a way we can better handle them so that they don't continue to grow hundreds of times faster than our ability to clean up the noise?
As one of answerers points out, for non-moderators, you'll only notice this problem if you frequent questions where there are a lot of comments. Since that's only .8%, of the total number of questions, it's unlikely you'll see it as often as a moderator would (since we get a higher amount of flags on questions that are popular or have problems, which tend to attract more comments).
Reasons why I think this is an issue:
As a moderator, I see a lot of flags from the system on long comment trains (20 or more comments in 3 days on a single post). Invariably, these comments contain clarifications that should be edited into their respective posts. Sometimes, these comments are even live debugging sessions.
I can say that I spend enough time on this issue a day that it's getting to the point where I want to just shy away from the '20 or more comments in three days' flag, and not even pay attention to them. I believe that's the wrong answer. I know why it happens, it happens because there's generally so much noise mixed in with the gems (that nobody bothered to curate into the place it should be) that it's exhausting to try to sanely moderate comments.
We tell people constantly that Stack Overflow is not a forum, it's a Q&A site. As a Q&A site, the focus is on asking Good questions and getting Good answers. If the answers aren't edited to include all information from the clarifications issued in the comments, then they aren't Good answers, are they? Likewise, if the question doesn't include all the relevant information, then it's not as helpful as it could be.
If Stack Overflow is not a forum, then shouldn't we treat comments like something that should be cleaned up regularly, to maintain the quality of the content on the site?
What I'm looking for are answers to help us solve this problem, or cogent arguments as to why these points are irrelevant, or not a problem.
Possible answers include: Better badges for cleaning up comments, warning Posters to edit their post instead of posting code / clarifications in comments, better handling of conversations between users (pushing those to chat), etc.