A high gloss surface is easier to clean. You see gloss used for interior trim in houses that gets a lot of touch and wear for that reason.
Walls, which get comparatively little touch, get a lower sheen.
If you aren't referring to sheen and are referring to the sparkle of metallic paint instead, I don't know either. I'm betting that it hides imperfections in the underlying surface better, but I really couldn't say.
I have read that white and yellow are super forgiving colors as well, which could be why you see a lot of non-metallic white on fleet vehicles.
