I know some of this is already covered, but my thoughts in my own words on the subject.

If your opponent only has 1 more point to win the match, then for you - it is beter to double early so the game with worth 2 points so if you do win, you will win twice as many points. (If you lose - well no mater if it is worth 1 or 2 points, you will lose the match.)

If your opponent only has 1 more point to win the match, and lets say you wait for a few moves into the game before you double - then your opponent has the basicly "free" oppertunity to either accept or deny the double and get to play again - and only giving you 1 point. That is your opponent only needs 1 point to win, and if he is already in a losing position, there is no point in him accepting a double - it is beter to just give you the point and start the next game. (Where as if you doubled early, he would already be in the losing game worth 2 points)

(This is of course after the Crawford match where 1 game is played without the cube)