All renderings eventually end up in Photoshop for compositing. Vray elements are saved with the rendering as EXR files. These elements are opened in Photoshop as layers using an import plugin such as ProEXR or Exr-OI. Without the plugin Photoshop will still open the file but without the extra layers.
If you download and render out an EXR file from my 'Studio Scene File' post you’ll end up with a teapot rendering containing layers as seen on the right:
I modify these Vray elements to create separate ground reflection and shadow layers that are separate from the product teapot. Also, additional elements can be added to mask out objects, textures, or enhance elements like object reflections and refractions.
This ground plane technique is not perfect and there can be a small halo between the object and ground shadows. The halo can be quickly painted out in Photoshop though, and this single render pass setup is faster than the alternative of multiple passes for object, shadow, and reflection.
Here is the processed Photoshop file: StudioSceneTeapot.psd
