I wear a helmet whenever I'm bicycling and I think I might fall and hit my head. My reaction time has simply increased as I have grown older, and I no longer have time to put my helmet on once I start to fall. So yes, all the time. Heck, I crashed six weeks ago going slow when I accidentally ran onto the grass shoulder and I made too quick my return onto the pavement. No cars, no dogs, just operator error. Head injuries are not good. Helmets can reduce the severity of head injuries.