Okay, winterberries give us bright colors during a gray time of year. That's reason enough.
But there's another reason. In the first week of April each year, cedar waxwings strip the plants of their long-lasting fruits. The berries are said to be too hard and sour for the birds until about early spring--when most food sources are scarce.
So, it's a great idea to plant winterberries--but research at University of Rhode Island suggests that it's even better to also offer arrowwood viburnums, highbush blueberries, serviceberries, bayberries, elderberries, chokecherries, and native raspberries. See the study reference below.