Basically the same as the elevator scale. The idea is just to make it a little less sensitive around center. The rudder I have set for 100%, but you probably would not want that for a twisty stick, for instance.
This is a very individual thing and no one will find the exact same setting to be ideal and will want some change to suit them personally. However, it does serve as a fairly good means of taming the gun of your tank as way of example.