Basically one sketch determines the length, then a variable section sweep is inserted. Normally with this feature a constant profile follows a path (or you go from one profile to another), but with the equations in the sketcher, the profile is constantly changing. Thus there is a nice wavy surface generated. You might find it useful for all sorts of surfacing projects. To make the feature wider you can pattern the surface, or you can add more segments to the sketch. It's probably easier to redraw it or remove the sketcher relations first though.