I mount one when I go to bed every night (And then I put a light on my XD 9!)
The light is a benefit because I don't have to carry that heavy Maglight in one hand and the pistola in the other. I didn't buy one with a flash switch on it, because dazzling a bad guy in my house will consist of perforating his rib cage many, many times.
It goes on only when I go to bed because I carry at 1:00 in an Uncle Mike's IWB holster, and the light won't fit. Bear in mind, if you're working for a security company, that you'll have to draw down on your target to see it. I'm not an LEO, but I've played one in the military.
"Guns don't kill people. Male Kennedy's kill people."