Dual rates are great for when you want to be SMOOTH. the normal rate, would be the 100% (+/- 5% if possible on the computer... its just better that way) Then the alternate would be as low as 30%. Take off at full throws and turn the dual rate on for high speed runs where full throw would rip a wing off.

Or for the 3D guy... the tamer rate woud be where he takes off and lands "trainer style" and the higher rrate would be the all-out maximum throws for the extreme maneuvers.

Or... you can just program exponential to make the center of the stick "soft" and still have full throw available. (my norm is to use this... normal rate is 100% throw ,no expo, DR turns on the expo, still 100% throw.)

You normally don't use EPA on the flight control surfaces... EPA is more normally used with throttle to allow you to get full throttle and idle shut-off wihtout having to spend 2 hours messing with linkages to prevent the stupid servo from binding. on the carb's stops.

So we are talking about 4 different things here....

EPA (end point adjustment)

ATV (adjustable travel volume)

DR (Dual Rates)

Expo (Exponential control response to stick position)