they can’t trigger on the edit event as there are too many legit uses of it.
They definitely do, I’ve experienced it firsthand: I mass edited all my comments to “[deleted]” and many of them got edited back within 2-3 days. There are some reasonable explanations about buggy caches, but that’s a really convenient bug for Reddit right now.
Lower bandwidth for who? When images are cached on other instances, it allows two things: