As a team it has some correlation to offensive success but for individual players, it's often pretty useless until you get to the outlier players (Miggy/Mauer on one end, Mendoza-types on the other). It's hard (impossible, really) to have a .330 average and a bad season and it's very difficult to have a .200 average and a good season. Spread out over an entire team, you're going to have your plus/minus power and OBP guys (in most cases, anyway), which balances out the weaknesses of using only BA to evaluate total offense.