Why to double?

Count after how many rolls you hit on of your opponents blots and you have a 4 to 2 advantage. And at that score you make gamons for white worthless.....

The match score is critical here. 4-away, 2-away is one of the more counterintuitive match scores. Basically you can double this score as the trailer even if you are not favored to win, and this position is a good example of why. You have reasonably high gammon chances and you do not want to risk losing your market and becoming too good - winning a gammon with the centered cube only evens the match; gammoning after doubling wins the match. That’s true of any 4-away score, but at 2-away, your opponent has a dead cube and worthless gammons. That means you can (and should!) play aggressively after a double/take to go for gammon. You also can get yourself into back games that ordinarily would have poor equity. In many such games, you are actually a favorite to win, but have negative equity because you almost always lose gammon or backgammon when you lose. Well, that’s no longer a problem in this case since gammons don’t matter for your opponent.

The practical upshot is that you can go gung ho to close out one or two opponent checkers quickly to win the match, but have some good winning chances to even the match if it doesn’t go well with the attack. None of this happens if you fail to double and roll, say 55. You will have lost your market and will have to play on for gammon. Further you must then be concerned about losing gammon yourself. You’re much better off after doubling.

Good and understandable comments. Thank you very much!