I have the same question, but i think Houska meant a normal plane, not the actual floor, background or foreground object..(as i know it does not work)
In all standard visuals, we add a plane for a background. Example: You have an interior shot & you see something through the window...
We need to add a texture on it, but it is black when you add a standard texture on. If you make it a light material, it;s doesnt work either.
How can we get it working?