playBunny: The reason to finish a jigsaw is to look at the picture I assume, perhaps show to others?

Anyway this is clearly an aesthetic endeavor, whereas a game of backgammon is a contest. Once the contest is over it should be ended. Better yet, the next frame should be started so that the moves actually mean something.

Again, chess is set up this way (we don't need to actually capture the king) as are most sporting events (we don't play all 7 games in a series once one team wins 4) etc.