I can think of: comments in torrent trackers, where comments sometimes provide useful information; and, if this even counts, forum sites, like Reddit or HN, where comments host discussions.
There were sometimes helpful corrections, but those came largely through email anyway, and, since I update the articles when I receive a correction, the corrective comments instantly became obsolete.
I just remembered the biggest reason why I removed comments: Spam. The added value wasn't significant enough (due to the reasons above) to warrant spending the time I spent removing span comments. Make a popular post and you'll get a whole bunch of "What a great post! Check out my thing: <thing>". I didn't want to spend more time moderating so I just disabled comments.
I’ve certainly found that useful more than once.
Comment sections are especially good for sites which the author doesn't update, so you can read the correction in the comment.