This whole issue is a sore spot for me. Seems like I've always had someone who missed their deadlines but "cleaned up" something that didn't need cleaning up. I've even done it myself. It's an easy trap to fall into, after all, we tend to be optimizers, maximizers, and perfectionists.
The best approach to this I've ever found is the solicit agreement to a few simple rules and standards. Things like:
- Don't fix it unless it's broken.
- Don't delete any code. Ever. (Did I say ever.)
- Don't bypass tools we've agreed to use.
- Don't violate standards we've agreed to follow.
- Quick and dirty isn't quick. It's only dirty.
Often the violator doesn't even realize what he's done until you point it out. OP was obviously a caricature, but you still gotta stay on top of it.