It's been awhile since I used one, but there were a bunch of sites that would "undelete" reddit comments. Which is super helpful because redditors seem to have a habit of retroactively deleting everything they posted, and deleted comments sometimes answer some question you're trying to figure out (e.g. (someone asks my question) -> [deleted comment] -> thanks! that fixed it!).
You can also search your own username and see what has been 'removed' by mods - much easier than signing out of your account and trying to find content that isn't there