The router skis are operated from the end cheeks, this give a great deal of mechanical advantage, it gives the operator COMPLETE control of the router. For most operations the router is locked at the centre of the rails but there are occasions like when planing a board that is too wide for the skis to fully cover the surface, in which case the router is slid then locked over to one side then to complete the surface it is slid to the other end and locked. The attached photo. illustrates this.
Nothing but heaven itself is better than a friend who is really a friend. - Plautus