I sometimes find typos in my own profile posts and it is kinda annoying that we can not edit it.
In conversations, however, I would not allow editing messages. I could, for example, start a conversation with you and insult you. You could "defend" yourself by insulting me back. I then edit my message with insults to something nice and report you for insulting me via private message. :confused1:
To my knowlegde, they used to allow members to edit their posts a long long time ago, but it would be constantly abused. Someone would post something offensive or against the rules, someone else would report it, and it would be edited before staff could see it, so they disallowed editing.