Paul,

Absolutely necessary: No. Beneficial: Yes. This is called differential travel. The longer up stroke does two things for you. One, it reduces the tendency toward adverse yaw (pointing of the nose in the opposite direction of the intended turn). It also reduces the chance of tip stalling at high angles of attack (low flight speeds). You can easily do it mechanically if you have a 2 servo set up by locating the servo arm angled out away from the aileron when setting up the control rod. With a single servo you can do the same thing, it is just a bit more tricky.

Clear?

Bedford