We are running an obsolete and chatty comment debt.
Anecdotally,1 very few of the extant comments on Stack Overflow (or any other Stack Exchange site) are rude, offensive, or spam. That's a testament to the rousing success of our flagging system. Over the years, the rate of rude or offensive comment flags to new comments on Stack Overflow has stabilized2 to between 0.1 and 0.15%:
The absolute number of rude and offensive comments posted to the site has increased as time has gone on, but flagging of such comments seems to have kept pace easily enough. There is no particular problem with excessively rude comments on our sites. However, when I read questions on the site, there's no question that many of the comments I see are obsolete or chatty. My subjective estimate is that somewhere between a quarter and a third of all comments have been overtaken by events or are little more than social pleasantries. Here's how the flag rate on those comments has progressed:
Note that the heavy spike of activity starting in September of 2011 coincides with the introduction of several flagging-related badges on August 28 of that year. The spike is a testament to the temporary power of extrinsic motivation. It also shows that there were plenty of existing obsolete and chatty comments available for people to flag. (Note, that all data includes helpful flags only.) The drop off in flagging rate likely has more to do with people earning their badges and no longer feeling the need to flag such comments.3
In the last year or so, obsolete and chatty flagged comments have increased from about 0.1% to nearly 0.5% last month. Even so, that seems subjectively at least an order and a half of magnitude off from the actual rate such comments are being added to posts. Assuming commenting has not improved substantially, we are racking up a considerable debt of obsolete and chatty comments. Here is the number of new comments and comment flags being added each month4:
Why should we care?
The trouble with this theory is that it doesn't seem like a big deal if you happen to think these comments aren't such a big deal. But there are two reasons we should be concerned:
- Broken windows
Many people see these sorts of comments as unsightly and encouraging of more of the same. The current system leaves most people no option other than flagging to clean up trivial comments. That results in a sense of powerlessness which is very unusual on a Stack Exchange site. Even if you disagree that there are broken windows, you have to agree that some people are annoyed by trivial comment clutter and (because of the deficit we are running) will never be satisfied. We have a system (comment flags) that barely scratches the surface of the problem. Flagging rude comments works. Flagging trivial comments does not.
- Moderator time
Last month, we saw ½ million posts with a million comments. There were 188,109 total helpful flags of which 9,985 were on comments:
3722 Comment Obsolete 3618 Comment Not Constructive Or Off Topic 1179 Comment Too Chatty 990 Comment Rude Or Offensive 476 Comment Other
So if you don't think keeping obsolete and chatty comments visible is a big deal, moderators are wasting substantially more time dealing with trivial flags than with flags on outright rude comments. No matter how you feel about trivial comments, we are asking our moderators to clean the Augean Stables with teaspoons. Ought we not free them up to focus on important flags?
Testing a comment hiding scheme.
When testing a comment hiding scheme, count it success when the test group raises:
- Fewer obsolete and chatty flags, and
- No change in the rate of rude and offensive flags.
Not constructive or off topic and Other flags are ambiguous. It may be that simply hiding rather than deleting such comments will be an acceptable result. I would suggest that comments would need to be displayed for at least a day or two in order to satisfy the second condition.
1. Which is to say, in my subjective opinion. 2. There are two spikes in the first half of the graph. The first, I believe is the natural enthusiasm that comes from a new button to push. The second is likely related to the [improved flagging](http://blog.stackoverflow.com/2011/01/improved-flagging/) introduced during January of 2011. The substantial drop off in flagging during May, 2011 is likely a result of splitting comment flags into several new buckets, but I don't immediately see where (or if) that was announced. Obsolete and chatty flags begin in that month. 3. I believe that I can verify this by comparing the number of people who earned the badges to this graph. But I don't think this is a critical part of the argument. Even if badges had nothing to do with this spike, the fact that these flags have not stabilized is a red flag (so to speak). 4. I'm including _all_ helpful comment flags on this graph since comment flags seem not to have been categorized early on. Flags and deleted comments are not exported to the public data dumps. But you can verify the basic shape of the comment graph using [this query](http://data.stackexchange.com/stackoverflow/query/153354/comments-by-month#graph). 
