Unity Skeletal Animation Performance Question

Hello,

I don't know if this question has already been answered but I can't find an answer so here goes...

It says in the Unity manual that an ideal number of bones is about 30. Preferably lower for mobile. In Blender and Im sure other 3D apps riggers often create quite a few bones for controlling the armature rather then deforming the mesh.

For example the armature that actually deforms the mesh may have 20 bones but there are another 30 just for controlling the armature that don't have any effect on the mesh itself.

So my question is does the performance in Unity rely on mesh deformation bones only or do controller bones cause a performance decrease aswell?

Thanks for your time!