You only have to look at the many statistics to get an inkling that there is a depth to it that isn't immediately apparent e.g. the manager will know that the batter after the next one is susceptible to flyballing a slow pitch from a left-handed pictcher on a wet thurday evening in the 9th innings when there are runners on the 2nd and 3rd bases, and will use the bullpen appropriately to maximise the chance of getting him out.