The Route-a-Pocket mounting plate is not required but can save time when working with smaller workpieces.  Once the Route-a-Pocket is "snapped" into the mounting plate, tightening the Route-a-Pocket's thumb screw not only secures the Route-a-Pocket to the workpiece, it also secures the workpiece to the workbench (see the Route-a-Pocket User Manual for additional information).