Paul,
I like to use low rates on takeoff and medium rates on landings with my new Extra. The reason for low rates on Takeoff is so I don't accidentally overcontrol the aircraft by using too much elevator or rudder. I like using medium rates for landings because you don't have as much airflow over the tail due to the lower engine speed, and you need enough control to keep the nose up when flaring. In addition, you are already in the air and have adjusted to the high rates, so you shouldn't be worried about overcontrolling the plane. I think you probably won't need three rates for Warbird flying, but it is nice for aerobatics. I have a 9C and absolutely love it, and so will you.

Backwing, a Rate basically means how much the control surfaces move when you move the sticks on the transmitter. Low rate = little movement, and high rate = lots of movement.