Pole Target

• The IK chain must have an initial rotation in the rest pose, and not just be a straight chain, for this feature to work well. Note that it is a good habit to do this regardless if a pole target is used, to guide the IK solver in the right direction and make it give more predictable results.

• Pole target does not work for tree IK, with multiple IK constraints being solved at once, since in this case the roll of the IK chain is already defined by the multiple targets, it is only for a single IK target that this degree of freedom exists.
• Degrees of freedom and limits for the first bone will be ignored, aiming the chain at the pole targets works completely separate of IK solving, rotating the chain as a whole, and hence does not use any of these settings.

Example .blend file.