I have seen an error several times recently, so want to alert those less experienced with the cube how to avoid the error.
The Crawford rule says that when one player reached match point for that next game (but only that next game) the cube can not be used.
Example: in a three point match my opp. gets me 0-2. I can not double the next game.
However, if I win the next game for 1 pt. The match is now 1-2. In almost all situations I should double at my first opportunity as described below.
My objective is to win the match 3-2 with as little effort as possible. If I immediately double, I will only need to win the next game to win the match. If I don't double I either need to gammon to win or play and win a second game, both harder tasks.
What is my downside. If I lose or am gammoned, I lose by more -- who cares?
If you are the person winning should you always accept the proposed double. NO! Only accept if you are ahead at that point in the game. You have a free pass and can play another game (score now 2-2) where you have a 50% chance of winning (assuming equal strength). That is why it is important for the underdog to double as soon as possible to minimize the lost position when there is a drop.
There are some advanced technical reasons when an immediate double is not right. For almost all of us (including yours truly) the occassional minor error of doubling too early at 1-2 is grossly outweighed by the error of not doubling immediately.
In longer matches the same theory holds -- as the underdog -- just keep doubling until you have won, lost or attained double match point.