Green Screen Photography
Green screens were originally implemented for the motion picture industry as a method for making composite images. Today they are commonly used in local TV news broadcasts, where a reporter in the studio stands in front of a green screen, which is replaced with a news image.
For still photography, they are used for annual reports where board members that were not able to be photographed together appear together and to place people in front of exotic backgrounds. I've found them very helpful for pictures of small children and pets. Individual pictures of each subject looking perfect are combined into a perfect "family" shot. Since it takes less of the individual subject's time, it stays within their attention span, making the photo session more enjoyable for them.