A seatbelt once saved my life,literally, and I still broke it off the structure - but that's a different story. If a rollover is the slightest risk, wear the seatbelt. As a firefighter, I attended many too many rollover accidents of farm equipment, and road vehicles where the use of a seatbelt would have kept the victim near to the center of the machine, so it did not crush them. Sadly, human's natural reaction is to try to prevent an anticipated rollover, so sticking out some body part, thinking they have the strength to overcome the rollover forces. On your bicycle, fine, anything bigger, have yourself already held in centered against your own instincts!