Not much.

In closer and the paddles will catch less air, but they have less centrifugal and gyroscopic forces to overcome.
Further out and the paddles catch more air, but they have more centrifugal and gyroscopic forces to overcome.

Its not something I've heard of people playing with... Stock width seems to always be right.

However, people do play with weights on the flybar. Less weight at (near) the tip would allow faster cyclic response, but also less stability. People sometimes add weights to the flybar to add stability.

-Mark