I have the Futaba 6XAs radio in an LT-40 trainer. I started with -20% expo on the 3 primary flight controls and fairly low rates. I also had the CG in it's most forward recommended position. Now that I'm comfortable with the plane and doing some mild aerobatics, I've moved the CG ½" aft and bumped up the throws (via dual rates) but left the expo where it was.

The LT-40 when set up for a forward CG and low rates really doesn't need expo. It's a nice feature to have - as long as you're sure you haven't gone the opposite way.