It's also removal of "Unsprung" weight. Even in Drag Racing, it's important to keep your rear axle and all that hangs off it as light as possible . . If it's hanging by a suspension . .
Because this is weight that you cannot transfer, but is affected by all the forces that act on the roll center of the car . . plus, if there's any inclination to either "Wheel Hop" or tire shake, more unsprung weight excaberates the problem . .
Having a "Strong" rear end assembly doesn't necessarily mean it has to be heavy . .