Some folks would put more than one light on their AR for a couple reasons. Surefire lights are very modular and they serve a number of purposes. For example, if someone had an M900A mounted to the bottom and a M97xx mounted to the side, a M900 would be the CQB light, while the M97xx with its turbo head and specially focused bulb would be their long range light. Another example of why you would have two lights is one of the lights could have an IR filter over the bezel. If you were to do this, one light is a blinding white light, the other is used only when wearing Night Vision Devices. Clearly mounting two lights is not for everyone, but clearly mounting more than one light is advantageous for some whose "job it is to kill people who need killing." Quoted Wes from MSTN.