I just got this absurd example, where what (as far as I can tell) was just a suggestion adding indentation to a code block resulted in a diff that made it look as though almost all the code had been drastically rewritten:

This is a problem when reviewing these edits because if the user suggesting the edit has changed things other than the indentation, I need to be able to see and review them. In this case, I glanced over the diff, figured it looked like nothing but formatting had changed, and decided to trust the user's edit comment that made no mention of any changes other than code formatting.
But honestly, since I didn't carefully diff it line-by-line myself, I might have just approved all kinds of blatant vandalism, and if that's the case, then I'll probably never know that I did so.