All my projects any more have almost as many perennials as shrubs, right from the onset. Perennials are incredibly reliable. They flower most reliably and come in a wide variety of colors and sizes, from low-lying border plants to tall irises and Giant Shasta Daisies and grasses. The incredible variety of foilage and bloom color make them a “finishing touch” that separates the best contractors/designers from amateurs. What they really offer is variety and, thus, completion.
Perennials have been cultivated for centuries. They are our oldest plants and bear little, if any, resemblance to their antecedents. Because of their incredible changes and hybridization, most have become seedless. It means most of them can be divided for use elsewhere in a garden. The plants will expand, even get very territorially dominant, but can be divided every other year or so for placement elsewhere. Mums, Irises, even penstemmons, a favorite of mine, may be moved and replaced, adding to fill in, gradually, empty spots in a landscape.
I include grasses in the perennial category. It seems there is yet another new hybrid of grasses every year, just an amazing explosion of available and exotic-looking plants that has many using them more and more often. Clumped grasses have become a standard in many places and are gorgeous. Ranging in height and breadth, from the huge Pampas Grasses to the smaller Oat Grasses, the selection has become most fun.