Dual Rates

Dual rates are a quite handy addition to R/C controllers.
In the years past beginners would be advised to lower the extent of travel on their control surfaces by adjusting the notch the linkage would connect to on the horns.

This would make the plane 'easier' to fly by preventing all to sudden movement, but it was also harder to control in conditions where you'd need the extra travel (crosswind e.g.).
With dual rates you control the amount of travel in the RX, and, more importantly, you can switch between the modes with the flick of a switch, so if you find that the wind got worse after taking of, you can switch to 'normal' travel on the servo's to take her in for landing.