Originally Posted by CPMaverick

I found a BP for Peter Coors in the seatback pocket years ago, he was flying DEN-LAX in F on UA.

It's true that your BP contains all the information necessary for someone to change your seat or even cancel your ticket. Since there is little to no incentive for them to do so, I don't think it is a big risk, but definitely better to keep your BP close-at-hand.