For most people, Rodney is correct. At center, the cables are both tight regardless of the setup. When pulled to one side, the airflow from the plane's forward motion and/or the prop blast keeps tension on the pulling cable and the offside cable has nothing to do.

However, if your flying style involves tail slides with the power off, the reverse airflow on the rudder could cause the rudder to pull up the slack on the offside, thereby slightly increasing the rudder deflection. So there is one (admittedly unusual) situation where you might want to have both cables taught all the time.

Jim