Exponential functions are great where they're appropriate, but probably not on the throttle. MinnFlyer's suggestion is much more akin to a multi-point mix.

Expo changes the amount of travel for different amounts of stick movements. Think of a stick having ten different positions to the right and ten to the left. A linear setup results in a servo moving one step for every step that the stick moves. Expo changes that. You can set it up so that movements closer to the center of the stick result in less movement of the servo. One step to the left on the stick might result in 1/2 step to the left on the servo. Because of the exponential nature of the function, steps further from the center of the stick result in greater amounts of movement of the servo. With a given expo curve you might hit a linear 1:1 movement only at step five to the right or left, with steps closer to the center resulting in less servo movement. Steps beyond five result in more servo movement, increasing as one gets further to the limits of the stick. At step ten on the stick, you might have something like a 1:2 movement, where when moving between the ninth or tenth step of the stick your servo moves from position eight to position ten.

In other words, close to the center of the stick the movements of the servo are less than proportional, while towards the extremes the servo movements are more than proportional. It's helpful for "softening" the sticks around the center, and often makes for smoother flying. I use expo in lieu of dual rates. I tend to think that dual rates are just accidents waiting to happen.

Expo on a throttle would not be useful.

Multi-point mixes, however, can be useful. If your engine's throttle response isn't linear, you create a mix that makes the throttle response linear by making the servo move shorter or further distances at different points along the stick's position. It's not a common thing to do.