You may want a joint to definitely not move when performing a solve (joint is sensitive / broken or you only want to move an arm not the body, etc). This could be a coarse option at the joint or an option per-DoF. Arguably "targetPose" and "restPose" could also be applied per-DoF separately but it becomes more complex to do so. Simply locking the full joint would be good initial option.
You may want a joint to definitely not move when performing a solve (joint is sensitive / broken or you only want to move an arm not the body, etc). This could be a coarse option at the joint or an option per-DoF. Arguably "targetPose" and "restPose" could also be applied per-DoF separately but it becomes more complex to do so. Simply locking the full joint would be good initial option.