For example, in a fighting game, you would want a general collision box around their body, then individual ones (hands, feet, torso, head), to check what part of what person attacked the other.
At the moment, doing that check manually is pretty brutal.
I think it might come in handy for lots of projects, and wouldn't be growing on the current collision system that much.
Note: I don't actually need it for a project I'm currently working on, so don't stress yourself. It's just a friendly suggestion.