If it makes the plane feel sluggish or sloppy, then you have too much expo or not enough control throw to make it worth while, or you have a sloppy control linkage or other control system issue. Probibly too much expo.

Too much expo tends to make the plane feel like it has "all or nothing" controls as well. You move the stick, and nothing happens, then all of a sudden, everything happens.

Keep in mind that because of the rotational nature of the servo arm's movement, a normal "linear" servo response results in "Futuaba positive" expo by nature, ie, the controls are more sensitive around neutral and less sensitive at the extremes. A small amount of expo will make the control response actually be linear, and even more expo softens the middle.

I use expo on most of my planes. Usually 25-50%, depending on the plane, and what I'm doing with it.