I wear one (most of the time) because I've had my bell rung a few times. If it ever happens again, I don't want to have to explain to the various medical providers and to my wife why I didn't have one on. That said, I have serious reservations about how effective bicycle helmets are in reducing concussions. Mine all occurred while I was wearing a helmet. My worst was a zero MPH fall while trying to get a recumbent tandem launched. If a safety device can't protect from that kind of accident, how beneficial can it be?