Many gardeners cut their borders back to bare soil in autumn. While this looks neat, it strips the garden of winter beauty and removes food and shelter for birds and insects. Leaving seedheads and grasses standing creates a winter wonderland when touched by frost.
Seedheads of Echinacea and Rudbeckia provide dark structures that contrast with golden grasses. Evergreen ferns and Bergenia leaves provide green form. Birds will visit to feed on the seeds, and insects will hibernate inside hollow flower stems. In spring, you can cut them back to make room for new growth.