About this tight!!! OK, got the smartass over with. With digital servos I tighten them up on both sides and sometimes get a bit of that servo hummmm but not tight enough for the servo to be jumping or centering. I allow no slack at all but it's a feel kind of thing. I set it up with the plane turned on so I can hear and feel what the servo is doing. When I think I have it I try to move the rudder by hand then I can feel the tension on the servo.
Does that make any sense at all. I want the servo to hold the rudder in place during flight without moving. You can get the digital humm with just the added weight of a control rod so it's more of a feel thing.