PaulS:
I've never understood this practice. Moving weight away from the CG means that more torque is required to move the weight. More torque means bigger motors, which means slower motors, as bigger motors take more time to get moving.
That's actually the point. If you read between the lines on a few of the statements this juggler makes, it's easier to balance things with a higher center of gravity than a lower one. This is because when you balance something on your hand or a robot on its wheels, you can't apply any force to the top (otherwise that's hanging, not balancing, a much less impressive feat). Since the top can't be controlled, you need to move the bottom to keep it under the COG. You want the bottom light and quick, and the top heavy and slow.