A fresh look at the kernel's device model

I can see how this is possible. I'm having trouble seeing how it is useful. Is there an example I can look at?

I can almost imagine that a bus might be able to include some of its devices in one class and some in another class. But I think I would either just make them different types, or have two related devices, one in the bus one in the class. Maybe an example will help clarify for me.

Thanks!