What the heck is a V-Ray Switch Material anyway? If you have never had the opportunity to use the VRay Switch, this video is a great way to understand what it is and how to use it in production.
a look at the V-Ray switch material which we would render using the GPU
You can looks at V-Ray Switch material is a kind of container. A container that can hold multiple materials at once. Then you can associate each material within the container to a numerical value from 1 to 10. You can then simply choose a material at render time by choosing a value. The V-Ray Switch can also show multiple materials at one time on a single object by sampling values from a greyscale texture or a ramp.
When would you use a switch? One scenario would be to have only one V-Ray switch material, that can have all the materials for multiple objects. Then using a V-Ray Scalar node, yo can distribute the various materials to all your objects in the scene.