A well-appointed garden needs not only flowers but also decorative foliage that is concurrently available to combine with the garden flowers in a vase.
The word derives from the Greek word xeros, which means dry.
At certain times of the year we just don’t have quite enough flowers. This is when "filler" is really important.
Unless the foliage of other perennials grows up to mask the bulb foliage as it decays, the garden looks a mess.
In the dog days of summer, walking through the garden is certainly preferable to working in it.