Limits and Stiffness
It is desireable to have control over how much bones in your skeleton can rotate in any given direction. This is an active area of development in Power IK.
Note: Angular joint limits are currently in active development and are not yet supported in Power IK.
Until joint limits are released, you can achieve a similar result using Bend Directions, which are currently supported.
Note: Joint stiffness is currently in active development and is experimental.
As of v1.3, Power IK adds basic support for joint stiffness. The feature is being actively developed and may node provide expected results in all cases yet.