There's this new feature* that Moderators (and maybe Janitors for now?) can see all deleted comments, even ones deleted by the user that made them. I see a lot of weird stuff that posters later decided wasn't fit for the public after posting. Not to mention it ruins my old technique of deleting a comment and replacing it rather than letting people know I'm weird enough to actually keep track of my comments and decide to change them, like, days later sometimes (only when they haven't been replied to, that is).
*I assume it's new because I've only been seeing them for about half of my short Moderator career and my comment history isn't stuffed full of them.