1) Anyone can buy a Surefire, including bad guys. 2) Leaving a bright light on for long periods of time makes you a target. Use sparingly for your night vision's sake.
I think PB is getting at the target ID thing. A good point. I keep a Surefire at the bedside and frankly with me in the car. Even in broad daylight I have startled a few bums getting too close to me at a stop light.
Might want to look into adding a light to the shotgun.