I think it is only relevant for base figures. It would not make sense for conforming figures since it essentially locks endparts in place which would defeat the conforming part

Here is portion of what the manual says about IK:

The extremity moves, and IK determines how the objects joined to it must respond in order to support the new placement. If you raise your hand straight out to the side, your hand, arm, and shoulder must move to accommodate your hand’s new position. Or if someone was to grab your hand and push, your arm would bend while your body remains still.

Poser supports IK for the arms and legs. With IK enabled, you can translate the hands and feet and achieve appropriate arm and leg positions automatically. IK creates targets to indicate the end of the chain. When the hands or feet move, the target is set to its new position. Moving any other body part keeps the target in its original position relative to the rest of the body. Once the target is reached, the end of the chain is fixed and the other parts must bend to accommodate the hand or foot position. For example, a foot reaches its target and the knee bends.