I was working on fixing a 3D character's forearm twisting and i wasn't sure whether i needed to have a joint unparented from its parent inorder to customize its rotations. That is since when we parent something we automatically pick up parents rotation by default.
Well its possible to have a joint parented to another but not follow its rotation. just needs a little math. first subtract out the parents rotation (using expression or multiply divide/plus minus node).
Now we can say how we want the joint to rotate by adding a value. So we could use the parents rotation or we could use some other object to drive the childs rotation.
I also was trying to integrate a new joint into an exisiting skin setup but i wanted the new joint to take away all the weights from a particular joint. Check out Brendan Ross's abWeightLifter at (supercrumbly dot com). It was amazing at moving weight from one joint to another.
Brendan Ross (supercrumbly dot com)
Jason Schleifer's Animated Friendly Rigging (jasonschleifer dot com)