the control rig and ik rig are 2 different things entirely. the control rig is just a defined component for moving characters. it allows you to separate types of animating cleanly such as driving vs on foot, vs on a bike. each of these might have their own requirements or lack of requirements when compared with each other. on a bike you may not need the hands to ever leave the bars so you might just use the bar positions with an ik solver( see further for explanation). by default a (the mannequin) control rig is using fk and ik for the hands and feet (if you lower the hips the feet are not pushed through the floor, they try to maintain their position on the ground) if you are animating it in sequencer for example. fk or foward kinematics is just bone hierarchy. ie the shoulder moves then the bones below it also move. ik or inverse kinematics takes a placement value and solves for the bone location back up the chain. for example when set up a hand ik will take the position of the hand and solve the position of the elbow bone and shoulder bone (and potentially the trap bone that controls between shoulder and neck). the interesting thing with ik is that you can live feed in targets to the animation bp and then to the control rig where you have ik set up to position limbs based on environmental factors. the most common use is for placing the feet on uneven ground or hands on appropriate positions when climbing walls. but, the possibilities are endless really. and you can build animations largely from ik placement data depending on the use case.
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