Binding means that a pushrod or a linkage is putting stress on the servo arm.
If the pushrod is bent or too short/too long because of the installation it might constantly pull or push on the servo arm making the servo motor fight to keep centered.

Adjusting the linkages is a way to get rid of the binding, e.g rotating the clevis to give more slack or tightening it. You can also change to a more appropriate lenght on the servo arm or bend the pushrod to releave stress.