The matte shader will occlude geometry behind the surface being rendered, however, the output image will have the alpha value specified. This allows for compositing tricks. When the matte shader is hit by shadow rays, the shadow amount determines how much of a shadow will be cast by the surface.
It is also possible to disable fog on the surface. This means that no fog will show up on the surface.
The following examples include this node.
This example shows how to create an atmosphere shader with volumetric shadows. The atmosphere object has a vex lit fog shader attached to it, and the spotlight has deep shadows enabled. The objects in the scene have a matte shader attached to them.