I've worn a helmet on and off for 20 years or more. It depends on the weather and where I'm riding. During the summer, I almost always wear my helmet (Bell Traverse) because my mirror is on it and, more importantly, it ventilates better than a ball cap. I'm not the slightest bit convinced it will save my life in a crash but I wear it most of the time because I rarely go outside without some sort of headwear anyway (usually, a ball cap). I'm not bald but I like keeping the sun off my face. Also, I ride alone either on bike trails or paths at recreational paces. But mostly, it's cooler than a ball cap in warm weather.