I think there should be a way to know what happened to our own comments when they disappear. If I have made comments on a post, I might never go back and check, or I might not notice that the comment was deleted. And if I do notice that it was deleted, I might not remember if I had deleted it myself, or it might have been deleted for me. If it was deleted for me it'd be great to see confirmation of that somewhere - not just for my own sanity (and faulting memory) but also to learn from it. If I know I didn't delete it myself, it would be good to know what the flag/delete reason was. Perhaps others saw something in my comment that I didn't, and knowing how it was perceived can only improve future comments.
I've seen this and this. The question was not migrated, I just really don't remember if I deleted the comment. If it was flagged or a moderator decided to delete it, it would be useful to have some type of accounting for that (especially if I can only see my own) instead of just purging them from the database and pretending they never existed (and coming here to harass the moderators on a case-by-case basis). I realize that comments are not the be-all end-all of the site, but I have this tracking for questions and answers, why can't we keep some kind history for comments as well (aside from the migration scenario, where I think it is often fine to blow all the comments away)?
We want people to use comments wisely, right? If we just delete them and don't tell anyone, the user may never notice they were deleted. So you succeeded in cleaning up that particular question, but you haven't succeeded in preventing that user from posting the same kind of comment tomorrow, and the next day, and the day after that, until they finally notice you're quietly cleaning up after them (or you send them a mod message to cut that sh*t out).