Sometimes users can make typos that they want to fix, or they feel like the original wall post didn't quite say what they wanted it to, and seeing as there are post limits, users may not want to waste a post correcting themselves. Being able to edit posts can fix that.
However, to prevent spam and typing different wall posts under the guise of "editing", there can also be an edit limit. Perhaps the same amount as a wall post limit.
I just think this could be useful for quite a few users.
