Do I understand correctly that the only reason to have a separate spin control other than rotating the body bone itself is just for the convenience of having the keyframes showing? Or are there other reasons?
Sorry if it's a silly question, but I started the rigging course too and now I can't seem to look at the ball and not think about the rig setup as well as the animation I'm attempting to practice.
It's about the ease of use for an animator. You don't want to have the top and bottom stretch controls flipping all over the place when you need the ball to squash and stretch in relation to the ground.
It's about separating the squash/stretch from the spin.
Hope that helps.