Center field is one of the most important positions in the game. A great defensive center fielder makes a great deal of difference to a poor defensive center fielder. That's just common sense. In the simplest of terms, if a great CF can get to a ball that a poor one can't, once a game, that's the difference of a hit a game. 162 hits.
That doesn't happen every game, but if it happens once every few games, it adds up.