Match Play. Red trails 0-1 to 5. How should Red play 21?
White has a strong broken prime and so Red should use the two to split the rear checkers with 24/22.
Many a general has found that fighting a war on two fronts doesn’t pay, especially when your opponent has the stronger position. Therefore, Red should play 8/7 with the ace, limiting his blots at a crucial moment in the game.
Any other move is at least an error.