Clockwise, Stretch and Anti-pop

Apart from the position of the controllers and the two Length properties, Limber gives you three other, keyframeable properties which affect limbs on IK:

Clockwise

The Clockwise property determines whether the limb bends out to the left or to the right. Usually it's left at either 100% or -100%.

Artwork by Daniel Savage. Limbs are Path with Foot from the Limb Library.

Stretch

If you turn off Stretch, a limb on IK will never be longer than it's two Length properties, even when you move the controllers a long way apart. You'll need a Locator to keep a hand or foot from being disconnected.

Anti-pop

Anti-pop can prevent visual pops and jerking that often happen with IK animation, when limbs snap straight or kink out too suddenly. It's especially useful for walk cycles.

Both legs have identical animation but the leg on the left has no Anti-pop, whilst the one on the right has Anti-pop set to 100%.