In more advance rig you will have the IK control bone, pole target bone along with the mechanic bones(Copy of some of the deform bones) and FK control bones(Another copy of some of the deform bones) that then can be switched between(Thru constraints on the deform bones and drivers). As a mater of fact, there’s a hotkey Shift+W->Deform that will toggle the deform option on all selected bones by default. You can use the adjust last operator(Bottom left corner of 3D Viewport or press F9) and change it to enable or disable.
