At minimum on the visible front side of the cabinets for sure. (biggerpockets.com)
To attach the other side of the cabinet door, add wood glue to the groove and a little on the ends where you will connect it to the rails. (housefulofhandmade.com)
In my old kitchen and in a kitchen we did for a client, we added end panels to the exposed sides of the cabinets. (domesticdeadline.com)