The illuminate you as a target thing is rather overblown outdoors. Except if you're using cover and not getting the light past the cover. Inside, virtually any light is going to reflect off walls and clearly show you as a target if there's someone to the side or behind you.

One thing the weapon mounted light will do is make you change your position after a round or two. The powder residue in the air pretty much blocks your vision. I think, but don't know, that the vision block is due to reflected light. Your training should have beaten turning the light off and moving after a round or two into you, but the light certainly forces the issue.