The bugs sip nectar from them, and I've seen mockingbirds investigate the berries. I guess they were eating them, but it was hard to tell through the window at that distance.
If you butterfly garden, Beautyberry is a two edged sword. Mocking birds like to EAT butterflies, so if we attract them with the bush we're declining our butterfly population. On the other hand, I had mockingbirds before I had Beautyberry bushes, and I figure that the more alternative food I provide for them, the fewer butterflies they'll eat, so I'll keep the beautyberries; they are pretty.
Beautyberry is also a Florida native plant, so I feel like I'm being a good environmental steward by keeping a couple of them.