What does the pinion snubber do ?

The pinion snubber takes advantage of the rotation of the axle housing. The housing rotates opposite of the wheels, because of the pinion gear. Under acceleration, the pinion gear tries to "climb" the ring gear. Since it cannot, it causes the housing to rotate. That rotation pushes the pinion snubber against the floor pushing the entire rear axle against the ground hard, raising the the rear of the car, while planting the tires. Depending which rear springs you run, the snubber may not even be necessary.