Hrqls: Good points.

The strategy of using the cube is subtle, despite its apparent simplicity. Like all plays in backgammon, it depends upon the odds of various outcomes. These are easier to illustrate if one assumes a "money" game is being played rather than a match of finite length. In a money game, the winner of each game wins an amount of money equal to the agreed stakes multiplied by the value of the cube. So, for example, if we are playing for $1 a game and you win a doubled gammon, I owe you $4. Each game is self-contained so there is no match winning strategy to consider.

Now, assume we are playing a money game for $1 a game and after several moves I offer you a double. (Assume we are of equal playing ability.) You examine the board situation and conclude that your chances of winning the current game are only 40%. Should you accept the double, or drop it (concede)?

The intuitive answer is to drop, because you are more likely to lose than to win, and accepting doubles the stakes. But surprisingly, the correct action is to take the double. This can be shown mathematically.

If you drop, you will lose $1 immediately. If you accept the double and play on, you have a 60% chance of losing $2 (net value of minus $1.20). However, you also have a 40% chance of winning $2 (net value of plus $0.80). Therefore, the total net value to you of accepting the double is minus $0.40. Since this is better than the minus $1 cost of dropping, you should accept and play on.

Accepting a double actually increases the net value of the game somewhat, because after accepting you are in possession of the cube and only you can make the next double. This turns out to be a very significant advantage in some cases.