We can flag questions, answers, and even comments for moderator attention, but we cannot flag a specific edit that has taken place.
For example, take a look at this question's revision history(+ see disclaimer below):
https://meta.stackoverflow.com/revisions/4380/list
While viewing the history, it would be nice if there was the ability to flag for moderator attention. Specifically during edit wars or when any user feels that the edits are unnecessary. Seeing as how any concern will require "moderator attention" for further action, this seems like a needed piece of functionality.
We can then in turn use the data from flagged edits to potentially identify users who seem to get flagged more than others in proportion to their overall number of edits. This will help in identifying potential misuse, abuse, etc.
**(+)**I completely picked this one at random and do not know if any one edit deserves to be flagged or requires it...
**EDIT**
I'm fully aware that you can flag a question/answer/comment already and that some feel that is the route to go for flagging edits as well. But we cannot derive from that any sort of useful data to determine if specific user's have their edits flagged more than others. We cannot determine if people are not using the functionality as well as others.