well history shows that it's good defense that wins championships. For teams with good defense, they generate their offense through their defense. The spurs for example play good defense, force the other teams to miss their shots and run with the rebound.
If you force your opponents into a half court game, the fast break points will be limited. That's the whole point of playoff basketball. To limit fast break points, to use up most of the 24 second clock before shooting with your half court offense and make sure you play defense. Playoff games usually comes down to the wire, so defense is more important in the playoffs than offense. You have to be able to stop your opponents from scoring in the last minutes of the games and if the other team cant score because of your defense and they dont have good defense to prevent you from scoring then you win.