Originally Posted by
wschruba
.... to allow the brake to pivot freely on the post.
Most cantis and v-brakes have a bushing mounted in the arms. The bushing is clamped firmly to the boss, and the arm pivots around the bushing.
I've only seen a grand total of two brakes that turned directly against the boss.
Unless you manage to tighten the screw hard enough to collapse the bushing, torque won't affect the turning ability of the brake arm.