Case in point: http://stackoverflow.com/posts/11643510/revisions
When improving upon an edit, and another edit is made before you submit, you are not notified that further editing has taken place and will overwrite all changes.
In this case it was a very small change and I was able to put it in quickly, so it doesn't actually show me overwriting.
I think a notification is needed. Someone else may have done a better job, spotted things you have not, or made changes that need to be incorporated into your own edit.
This is not a duplicate of: http://meta.stackexchange.com/questions/93697/race-condition-in-suggested-edit-approval?rq=1