Apart from what said from @MPD, I can see some more cases where editing could be (more) acceptable:

- Editing tags
- Removing tags from the title
- Reverting spamming (done from the user who wrote the post, or other users)
- Removing any name-calling (i.e. abusive language or insults) added to the post from any user, including the one who wrote the post
- Removing any comments about users added from any user, except when comments are about a given answer (which doesn't mean users are allowed to write "the user who gave the other answer is an idiot")

The first has more sense if done to remove a misused tag, especially when a tag is going to be removed; the second one could also be avoided, but I think it is more acceptable if the questions in the front page contain tags in the title.

Since the closed questions are queued to be valued to be (eventually) re-opened, edits on closed question needs to be more careful. For some of us, used to the times when editing a question would not queue it for review, the habit could be hard to forget. Still, if the edit is done with the mere purpose of queueing the question in the re-opening queue, it should be absolutely avoided.