Smooth skinning
Bones gives you the option to use masks to define the distortion mesh to get ultra-smooth skinning without any artifacts.

Pupeteer
Pupeteer allows you to control many instances of Bones from one layer.

Simplicity
Bones was created for an animation feature film, which required the animation of A LOT of characters.  Bones makes it super easy to setup and manage many different characters.

Less layers
With Bones, you can control a whole character on a single layer without needing any extra nulls or controllers. This keeps compositions tidy and light.

Speed
Bones is a native plugin and does not rely on expressions, so it is really fast. Oh, and it is also GPU accelerated, so it is really, really fast!