I agree with cheez. If run correctly, the press will turn more possessions into turnovers than the other defenses. If you go uptempo, you're trying to "beat" the press. There are times when that works, but if you're not insanely faster than the other team, you're essentially upping your turnovers even more. Meanwhile, if you go slowdown, you're minimizing the possessions, but the turnover ratio still has the risk of remaining the same, which kills the offense dead before the game starts.