They are for entities which are animated to move off or rotate on their pivot point such as flying characters, where limb hit detection would not otherwise register.
You really don't need these settings unless you have a reason to hit the entity and it has this specific kind of animation, for example only doors which use limb hit and the collision has been turned off in script. Most characters are moved around in the engine so do not need it to keep track of where limbs are located.
