The use of ShapeOrig

 So in Maya, every time you apply a deformer on a mesh, you'll immediately get an extra shape node of that new mesh, called "xxxxxShapeOrig".

This is Maya to tell you that your deformed mesh is based on this "original" mesh, and it took it as their own delta. 

What you can do with it? 
- Transfer new UVs without affecting the rig.
- Pre-deform certain mesh. (but this is slightly irrelevant because you can blendshape stacks. Creating extra nodes tho)