EDIT: I am not talking about moderator actions editing a member's posts, but when a member edits their own post.
It would need an option to send notification or not, as it would be annoying to receive notifications for minor typo corrections, but I think it would be good if you could opt to send notifications for any edits that add significantly to the post.
You could argue that if there is something significant then you should make a new posts however I think that often it can be useful to keep relevant information, argument points etc. together in the same post, especially true I believe for the post post in an information thread. For example in five minutes after I posted this I might think of another reason to argue why this is a good idea, and rather than spreading such posts around the thread it would be nice if they are all together in the OP, and people get notified of a new point.