Before the whole "light on a helmet" saga escalates let's not forget some folks run a headband light like a Petzl or some other small LED setup clipped on a rail or otherwise so you've got a small signature lamp for hands on tasks. Then you can see what you're doing without flooding the area with white light from a weapon light.
And then there are the SEAL guys who hang 2-3 strobes on their lid.
A light just like anything else requires discipline to use. Leave it on all them time and you're a BB magnet, plus you do truly piss of the rest of your team who don't enjoy being blinded or spotlighted when you look at them.
Airsoft, where nothing is hurt but feelings.