Big discussion happening at moment! Do you ever see this in normal comp play?
Jimmy Walker on 'backstopping' on Tour: 'If you like the guy you might leave [your ball] to help on a shot'
The act of “backstopping” is when players (consciously or not) don't mark their balls on the green, especially when their balls are close to the hole. This action (or inaction) gives other players in the group a small advantage should their balls strike the unmarked ball. Should the balls collide, the player who hit the resting ball plays from where his or her ball ended up, while the player who didn’t mark gets to replace his or her ball to its original location without a penalty.