A back game is when you have at least two (deep) anchors made in the opponents home board. Your opponent is bearing in and later bearing off against these anchors, trying to avoid to get hit. If he manages to get his men out you most likely will lose a gammon or even backgammon. So in general, you should not try to play a back game. Timing is a very important feature of every backgame, enabling you to hold your prime on your side of the board.
On the other hand, well timed backgames often produce many double shots and therefore many single wins for the player.