The PD where I live uses mounted lights on their Glocks and their M4s. Most officers in plain clothes don't have lights mounted due to concealment issues, but they carry a small light in their pocket or wherever. Safariland is the only company I am aware of that makes decent holsters for serious duty use that meets basic requirements like retention, appearance on the duty belt, etc. Even during daylight hours, an officer may need a light. Abandoned houses and the like used by criminals for whatever activity often don't have power (lights), nor do areas like crawl spaces, out-buildings, closed businesses, etc. Weapons lights should be used "conservatively" whenever possible- short flashes, and MOVE. You can't hit your target if you can't identify it, and you may engage the wrong target. $200 is cheap insurance for protection from people hiding in the dark or the fallout of an accidental shooting.