All year for me, having when younger came off and left a fair chunk of scalp on the (rough) tarmac and had concussion I prefer to wear one, realise it isnt the be all and end all in terms of safety, that would be some huge off roader but I think the helmet does protect against brain injury. A child at my kids school died hitting a kern when he fell off his bike, report said he would probably had survived had he been wearing a helmet.
Up to the individual, as it shoul stay.