I wear a helmet sometimes - like when training, group rides, etc - . If it were for my personal experience, I wouldn't bother at all about wearing one. In my only serious accident in nearly 50 years of riding (hit from behind by a drunk driver) I wasn't wearing a helmet, and had no head injuries except for some road rash. To be honest, I had a mild concussion but without any sequels. A helmet wouldn't have prevented my broken shoulder blade, badly sprained ankle and lots of body road rash.
I was wearing a cycling cap, but didn't start a thread by the title "Caps work!".