A light on a handgun has a very specific use. One, that if you're not LEO or .mil, you probably won't encounter.
As a civilian and something goes bump in the night you can search with a flashlight in your weak hand and keep your TLE in retention with your strong hand. This way, if that bump is your son you don't cover your son with your muzzle when you ID them. Remember, rule #1, never point your gun at something you're not willing to destroy.Also, you've just made it more difficult for that bad guy to keep track of you (move the flashlight around, flashlight techniques but that's a different thread) and with your gun in retention it is easier for you to retain your handgun if the situation goes to shit. Anything close enough to identify with the flashlight you ought to be able to engage one handed. Get a good surefire with a lanyard and you're all set.
Unless of course, you just want it for the Gee whizz bang factor.