When wheels lock (usually the rear), the locked wheels usually break loose from the pavement, and will want to go faster over the road than the non-locked wheels. If they are the rear wheels that go faster over the road, your UTV will go sideways. If you slow down and/or steer poorly, you will get a moment (a torque) that may tip you over--especially if the UTV is top-heavy.
I guess I'm getting confirmation bias to continue not to wear a helmet, especially when riding in my wooded 8 acres to collect downed trees and/or cut undergrowth, dead trees, etc.