Slopemeno hit the nail on the head with his thoughts on indirect lighting techniques.
"You don't have to point the weapon at the potential threat to get *some* illumination. Pointed at the walls, ceiling, or floor still gets you some light with no muzzle sweep."
Specifically, keep the weapon pointed in a safe direction, usually down, bump or turn on the on switch as needed. Also, the rule of thumb I agree with is "When in the dark, stay in the dark; when in the light, light up the dark."
Our house guns rotate between G-19's with attached lights or other handguns with a surefire that has a lanyard. I have trained extensively with both methods and they both have their ups and downs. Also, the lights we use for our Glocks snap off so can be used independantly if required.