Something like 40+% of all bicycle accidents known to society are single falls, for whatever reasons.
They CAN, and DO happen at ANY time.
To ALL kinds of riders.
Just the kind of thing where a helmet can do a lot of good.
If you're in a car, would you then only use the safety belt when speeding or when driving in poor conditions?
Trying to figure out WHEN you're gonna need a certain safety feature beforehand is NOT likely to be a successful, long-term method.
I don't need a helmet to save my life to use it.
I'd consider it money, comfort, and style well spent if all a life of helmet use would save me from is one split eyebrow with the associated trip to the ER, stitches, shots and all that.
If a helmet would prove even more beneficial, well, that would be a nice bonus.
I can't say I actively LIKE wearing a helmet. It's not like it gives me a buzz or something.
But the actual "cost", in money and comfort is so low, and the possible payout is so big, that it makes sense to me to use one anyhow.