Our Kodiak is used mostly on the farm so I tend not to wear a helmet when I'm zipping around here, but if I intend to go trail riding I will always wear my helmet, because you just never know what will happen, I've been hit in the head by big tree branches I didn't see (probably my fault), and I've even been thrown off and smashed a helmet on a rock, also when I was younger I joined the rollover club and did a number to my helmet, so had I not been wearing one I'm sure it would have hurt a lot more than just my pride.
I obviously don't know your definition of "crazy riding" but I think I'm a pretty relaxed rider and I've had some wicked things happen. So my vote goes to wearing a helmet, even if it isn't a full face it'll still protect you more than not wearing one at all if get into an accident.