Position 442

 How should White play 21 here:

It is good to make points in your outfield so you consider 13/10:

Although this move tidies up a blot, it fails to do anything about Black’s threat on their side of the board. In his book “Backgammon Opening Concepts”, Michy said that attacking with 10 checkers in the zone is strong, but attacking with 8 checkers in the zone is weak. Nine checkers in the zone falls somewhere in the middle, but I believe that when your opponent has 9 checkers in the zone it is good to anchor up. Here you need to anchor up 24/22, and playing 13/10 ignores the need to anchor.

Consider 24/22 10/9:

Moving 10/9 means that Black no longer hits you with as many rolls. Although it is nice to be hit with fewer rolls, this does nothing about increasing your advantage, namely building a stronger board.

Consider the correct 24/22 6/5:

If you are hit, you will have an anchor and return shots from the bar. If you are missed, then you will have your 5 point slotted and your board will be improving quickly.

Note that Black having 9 checkers in the zone was the driver for you playing 24/22, securing an anchor. The 22 point may not be the best anchor, but when you could be attacked , usually any anchor will do.

If the position is altered so that Black only has 8 checkers in the attack zone:  

     Now you do not need to anchor, so you can play 13/10, locking up your 10 point.