on my forum I give the members 15 minutes to delete the topic, and 30 to edit. I fugure that is sufficient enough. I have previously been members on forums long forgotten now, where they used to allow the users to do that and it certainly messed up the flow of things.
when i first opened up, I think i had triede this but i hadn't had an anti spam mod yet, so a spam user/bot or two got in, made a post and later edited a link, that lead to some quite objectionable material. I figure the 15/30 practice is sufficient. and if a member wants to still further edit it or have it removed, he/she can report it. or pm a mod or admin:)