ah well, Sammy was talking about road racing. It's not really my game but I do know that if ( when ) you come off, if you stay with the bike it will not hit you from behind, and also you present the smallest target, for the shortest time, to whatever is following. Road racing circuits don't have kerbs ( except at the TT ) and you can slide long distances at quite high speed with confidence, you just end up in the grass or gravel.
i've never done trials but I'd guess that you try and retain whaever control you can if you fall off.
in track racing you stay with the bike if you can, again it minimises the target for anyone who is behind you and stops the bike standing up again, grabbing some traction and flipping over on top of you.