Good question I don't have a perfect answer but, here goes. Adding some right thrust helps because there is always a left yaw component (except when the prop is not turning) and my guess is that designers likely target typical cruising power and airspeed or possibly some condition where excessive yaw and slow airspeed is risky. If you also add right rudder as the throttle is advanced it seems logical that it is going to be more than you need when you get to cruising speed because you also have the right thrust added to it. While transitioning to cruise speed or during touch and go practice it would be helpful but, once at cruise it is likely to cause a right yaw. Being able to turn it off would leave just the right thrust component. Here is an idea - why not add a gyro that senses the yaw axis and have it in the "normal" mode not the "heading hold" mode and every time you advance the throttle and the plane yaws left the gyro will correct with a momentary right rudder. Here is the best thread I have found on how our RC gyros really work in an airplane http://www.rcuniverse.com/forum/m_6056543/tm.htm. It is important to remember that if you use one of the new Heading Hold gyros you must switch it to the "normal" mode instead of the heading hold mode or you will find it difficult to change directions. This would be an alternative way of adding right rudder with the advantage that it does not engage when you don't need it. I need to add that I have not tried this except for doing loops and Cuban 8's. It could cause more problems than it solves. Great hobby

Howard