You win games by scoring more runs. You score more runs by winning more bases. Defensively, do everything possible to not allow bases.
Before seeing other posts, my first three thoughts were same as Rob T comments...
- you never know which way the ball will kick
- habit to instantly bust when no one on is way better than allowing for decision time
- know the field and what holes in the dugout need protected
To me, this all adds up to "bust".
For those commenting that it is rare that a play develops or a catcher does any good, I think we are ignoring the fact that when the catcher does his job and is there in the vicinity of the ball, the runner stays put and there is no play. That is the objective. So, we don't always register that a base was just won by the defense.