I thought I messed it up! I had no idea this was a thing.
It's bad enough trying to proof my own comments what with being navigated away from that comment (I've a few recent typos caught well outside edit windows which nag on me as I type). Changing submitter's content without notice is ... less than optimal.
I'll note that certain edit features (e.g., year edits) do involve a confirmation, which has in fact proved useful.