I agree with BB's explanation, and I did mention generating different VSS zones if nodes vary from zone to zone in the original model.  But you will not see any changes if you are just copying the same node arrangement from original to VSS unless you are applying to another wing model.  However, let's say you are adding something extra to your original model shaders, a better original node arrangement or from another model which enhances your feathers substantially, or realistically, then you would load that into VSS and synchronize it to your existing model.  Now, you have completely overhauled your model with a new set of shaders which should be better than the old set.