I like a weapon mounted light. It gives you one less thing to worry about (not carrying another thing). I prefer ones that have an activation different from a trigger pull. What I mean is that I've seen some AR foregrips with a light receptacle, but the light is actuated by using the weak hand's trigger pull. This could be a bad thing. In a stressful situation you might pull the light resulting in a sympathetic response with the other hand which would fire the rifle. That's why the light on my AR is actuated with a weak hand thumb push style button.
I hope that makes sense.