Matte shadow

A matte shadow material is essentially INVISIBLE.

So what is the point of it?

It’s good for product display shots.

Set up a gradient ramp background. Rotate it 90 degrees on U.

BTW, here is a tip on the rotation ... watch the UVW spinners as you rotate ... and keep the rotation icon circular.

Make a large plane for the matte-shadow:

Apply matte shadow to the plane with default to accept shadows:

You can even turn back the shadows, change their color:

Another use is to mask out objects in a background image and “hide” behind the background.

The matte shadow material is applied to the flat shape that matches some of the edges of this building.

The render: