The mix you are asking about helps to maintain our head speed in demanding maneuvers where lots of cyclic is being used (think continuous flips and rolls). It attempts to offset the additional drag that cyclic inputs create by increasing your throttle.
If you are using any kind of governor, this mix is unnecessary. I also wouldn't worry about setting up this mix if you are not into 3D.
Setting the values is trial and error. With the mix active, you should see the throttle increase slightly with applications of cyclic. Just set an arbitrary number in the mix and go fly. Then adjust the mix percentage as needed.