Comments are useful. Many, many posts need some small amount of meta discussion, and comments fulfill this need.
Comments are also noisy and distracting. Occasionally, someone will post an insightful and informative comment that complements the post its attached to... But more often, they're tangential, quickly irrelevant and in the way: stale comments show up first, making newer comments less visible.
The guidance here for a long time has been that comments are transient, "temporary Post-It notes". And yet, some do hang around for months or years because cleaning them up is a tedious, unrewarding job.
So let's fix that.
I propose that all comments older than 7 days be hidden by default unless the comment has been up-voted in the past 30 days. Hidden comments should be indicated by a note below the post ("add / show 3 more comments") and made visible to anyone who cares to click it.
This doesn't destroy anything, but it would get it out of the way of most readers - and hopefully encourage folks to edit it into the actual answers as a result.
Note: I previously suggested this here. Other similar ideas have been floated in the past. However, I'm not suggesting that comments be automatically deleted, and they should be hidden based purely on the age / activity of the comment itself, not of the post to which they're attached.