As a recumbent rider, I sometimes wear a helmet and sometimes don't. But I am absolutely fanatical about wearing elbow pads. If I drop my bike at any speed, those are the first things to hit the ground. Elbows hurt like hell and take a long time to heal if damaged. (Will there now have to be a locked Elbow Pad Thread? :-). When I do wear a helmet it is because of the following odd collection of reasons:
• Conspicuity - mine's white. (Yeah I know, no use in a snowstorm.)
• Somewhere convenient to mount an extra light - and no it doesn't create an extra injury hazard because 'knock-off mounting', a thing borrowed from my aeromodelling days using breakable rubber bands so that wings would fall off plane in the event of a severe prang instead of getting all smashed up. Not rocket science, aeroplane science.
• In winter I like a hat to keep my head warm, but most caps are too hot. Ventilated plastic hat = just right.
• In summer I like a hat to keep the sun off my pate and out of my eyes. Most cycling caps too hot. Ventilated plastic hat = just right. Just me.
I particularly like not wearing a helmet on cycle path trails on busy bank holiday weekends when everybody else is sweating in one for no apparent reason as we are all doing ZZZ miles an hour. Including unfortunate kids with necks like tulip-stems in heavy full-face BMX helmets because Mommy & Daddy Seh.
People are strange. Me included.
I keep a samurai helmet with gold 'deer horns' for special occasions. It has a face-mask with fierce grimace and huge fake moustaches. Makes small children cry and car drivers pull over, mail their keys to the nearest police station, shave their heads and take up a life of solitary meditation and good works.