Yes. The reasons are simple and mathematical: On this planet, it is dark about 50% of the time. Most of us sleep, or at least wind down during these periods, so an incident during a period of darkness will generally occur while we are not 100% mentally switched on. Additionally, often criminals like to take advantage of these periods of darkness. Turning the lights on may not be possible or a wise tactical position (time, exposure to hostiles, giving away your presence and position, or a power outage due to a savvy criminal or storm). Even during hours of daylight, you may need to search dark areas like storage sheds, basements, crawl spaces, closets, etc.). A light is crucial in these situations to identify your target and place accurate fire on that target, and to determine that what you are hearing is not a pet, a trash can banging on the outside of the house due to wind, a sleepwalking family member, etc. "Recon by fire" (shooting at movement, noises, or shadows) is not a sensible engagement method. You should also have a secondary light source (another light NOT mounted on a weapon) handy, as it isn't always appropriate to point a gun at everything. As with any defense tool, getting some training from a competent instructor can't be overstated- simply mounting your light and playing with it a little bit isn't enough. Along with periodic sustainment training. I even keep a light mounted on my S&W M&P 22 pistol, so I have the opportunity to do some "sustainment training" whenever possums show up and start stealing my outside cat's food.