This node is intended to use certain properties of a shader in other different material or texture setups as a reference.
how to use
Let's say you have 3 bottles (or more) and each of these bottles will be different colors but the bottle bodies will be in the same noise setup. In such cases, the "Ref Shader" is very useful. As you can see in the setup below, we have linked the "Noise texture" to the other two small bottles. So every change we make in the main Noise also affects the noise in the small bottles. Setup is simple and the below setup is belong to the big bottle. For the similar setup in other small bottles, you can simply plug the main noise from the big bottle to the small bottles. To do this just drag and drop the "Main Noise" from the big bottle to the small bottles' ref shader's link slot in the "Mix texture". You need to do this action from the Material Window (There is no way to to this from the Node Editor right now). It's a bit cumbersome but it's working. You can use this setup in many scenarios.
If you want to inspect the scene, you can download it from the link below.
Download the scene from this link
Info: The 3d Models in the scene obtained from the Cinema 4D's content browser except textures.
Info: You may need to refresh the scene from Live Viewer if the textures are not update.