I’ve gotten some questions about posters deleting their own comments lately, so here’s an explanation to the best of my knowledge.
After you post something, you can edit or delete it for 60 days. The edit history is tracked, and anyone can view it by clicking the pencil icon at the top right of the post. (Exception: if you edit within 5 minutes after posting, it won’t show up as an edit.)
Deleting something works the same way. Your post is changed to a message saying it’ll be removed in 24 hours unless someone flags it. During that time, anyone can still click the pencil icon to see what you’re deleting, so they can judge whether or not to flag it.
If no one flags the post, it’ll be hidden automatically. Hidden posts aren’t purged from the database; admins (and maybe moderators, if we had any?) can still see them.