Seems like people set them for a particular need such as BIF, portrait, etc. I have one set with settings based on shutter speed for BIF and the other for the aperture I use most. Real easy to change and as you said it does provide for a quick change.
Nobody should seek his own good, but the good of others. <><
I use U1 for birds in flight. I use U2 for indoors w no flash. It is set up w auto iso. I mostly just shoot Aperture priority and am not in U modes, but it's nice to quickly turn dial and be set up for something specific.
"Cameras and lenses are simply tools to place our unique vision on film. Concentrate on equipment and you'll take technically good photographs. Concentrate on seeing the light's magic colors and your images will stir the soul." Jack Dykinga