Ideally shot in a studio, virtual sets make it easy to change the sets and backgrounds viewers see when they watch TV shows without the production actually doing any physical changing of sets inside the studio. This is quite prevalent in news broadcasts and talk shows where both taped and live shows use partly or completely virtual sets coming from the computer. Instead of using physical sets and backgrounds, the virtual sets simply replace the blue screen behind the actors or hosts and other retained physical sets, which mostly include the furniture used by the on-camera talents, with computer-generated sets and backgrounds.
Blue screen effects are widely used in weather forecasts. Technically, a meteorologist simply stands in front of a blue screen during the broadcast and he looks at the video monitor on one side where the screen is already replaced by the weather map. This allows convenient pointing over the exact areas on the map during the forecast, even though the person talking about the weather update is only standing on a plain blue screen.
Mixing of live characters, props and sets with computer-generated imagery is widely done in film projects, especially in epic, fantasy, horror, action and adventure movies. Ideally, actors are shot on a blue background inside a studio, and then the screen gets replaced by another background such as a scenic vista, magical land or deep space. In some cases where an actor in an action scene is doing stunts, wearing a harness can provide the illusion of flight and other gravity-defying stunts. During post-production, the wires and the harness are more easily erased when the scene is shot in chroma.
Motion control photography allows the use of still or motion photography to make visual effects that can't be produced when only shooting the scene with a single camera or in a single shot. For instance, this may be used in a scene that needs to duplicate or combine multiple shots into a single shot, but it's impossible to shoot them as a single take. This technique needs precise control over a camera's movements and this is typically done with the subject shot over chroma or blue screen. This makes it easier to do post-production work with the shot as there are no distracting backgrounds over the subject when it gets manipulated for special effects purposes. Also, the blue background can simply be replaced by other visual effects intended for the scene.