Width adjustments change the sensitivity of the controls. A wider line spacing makes the controls faster, and of course closer spacing slows the controls. I have a Smoothie with lightning fast controls that my Dad built for me a few years ago, and it was so twitchy I really couldn't fly it well. Then my friend and flying mentor, Ed suggested moving the lines closer together with an adjustable handle, and that did the trick. An adjustable handle will really help dial in a plane to fly its best.
Don