Initially, Austin only recommended planting the weaker types in groupings to produce the look of a fuller, more desirable plant. I'm sure there is likely more than a little of the desire to increase sales, too. Decades ago, when faced with stagnant sales, the shampoo industry hit upon the famous "lather, rinse, repeat" slogan which resulted in sales doubling over night. Of course, if the product won't clean your hair with one application, a second isn't going to improve its performance. My experience with Constance and Gertrude was they were rather largish plants and required no assistance in appearing bigger. I would be concerned with the probable blood loss trying to groom and prune the mass of barbed wire which would result by planting multiple "Galloping Gerties" together. Constance produced the best for me grown as a climber so laterals could be encouraged to produce more blooms.