I in fact agree with richohealey on the expo... Yes, it is OK to "soften up" the rudderthrows on foamies and wild 3D-planes but I never use it on real RC-planes. (3D and foamies are NOT real models, they don`t fly like a plane...)

But on the other hand I use dual-rates the opposite way from richohealey on acromodels. On takeoff and landing I have the dualrates OFF to be able to correct for gusts. And when I start to fly acro I switch the dualrates ON to get the proper rudderthrows to suit my flying, throws that are small enough to be able to do unnoticeable (for the judges) corrections through loops, CubanEights, VerticalEights and so on. As an example I prefer the elevator throws to be so small that I use appr 3/4 of the stick-movement to perform a BIG loop. Which gives very smooth flying! And for the landing I of course need more elevator to be able to flare properly and to correct for gusts again.
I use my dual-rates a lot, switching through flights. And also they are a great help when testing a new model.