One of my first challenges in studio photography is to get the background pitch black. In my early attempts, even the use of a black cloth for backdrop doesn't always work. Now I know why; it is just the simple physics of light. Light falls off at inversely proportional to the square of the distance added. I have heard this preached many times when talking about how the flash works, but have not applied it to control the background exposure in a studio setting. (Note: since the sun is 93 million miles away from the subject, light falloff is hardly perceptible when shooting with daylight as the light source, either indoor or outdoor!)
The easiest way to apply this is to set the light source close to the subject and the background relatively far away. Kirk Tuck says in his book "Minimalist Lighting - Professional Techniques for Studio Photography":
"Background Control. Suppose you need your background to be much darker than your foreground (for, say, a portrait subject), and you hasve a limited amount of space and that back wall just isn't going to move any further. If you move your main light closer to the subject and adjust your exposure so that your subject is correctly exposed you'll find that the background will be darker. Falloff has worked to your advantage."
Here is where I don't want light to fall off quickly: group photography. I recently tried to shoot a group of 3 people in my studio and had difficulty getting even lighting. Now I know why. I would have needed to move the main light to the front, or use one light on each side of the group.