Shadows Only

There are many situations where it would be helpful to only render the shadows received upon an object rather than the whole material itself.  There is a simple way to do this within Material>Shadow section, shown below.  Simply check the Shadows Only box.

A perfect use case for this is the the scene below.  Let's say you want to go for a seamless background for your model.

Normally a scene like this would be render as follows with the floor plane showing up.

However, with the shadows only box checked, note how the plane disappears but the shadows still render, giving the effect of a seamless scene with a suzanne resting above a gray surface.