Many gardeners spend a lot of money each spring on annuals because they provide continuous colorful blooms in pots and beds from late spring into fall. If one has only perennials in the garden, it's harder to get perfect continuity of color.
Typically, perennials only bloom for a few weeks at a time so there needs to be a succession of overlapping blooming perennials across the entire growing season. That means having many different perennial plants in the yard. So most flower gardeners, even if they specialize in perennial plants, supplement with a few annuals to boost the amount of color.
Of course as fall comes, we know that a hard frost will kill off our annuals for good. However, there are few tricks we can try in order to get a bit more mileage from our annuals.