Ensemble casts are casts in which a number of characters are given equal status, rather than giving one performer star status, while the others act as supporting characters. In such a cast, a group of characters becomes important to viewers and listeners, giving the creators of the production a chance to play around with the characters and the story much more. These casts are especially common in the television industry, with shows like Lost, Arrested Development, Bones, Heroes, and Buffy the Vampire Slayer using the ensemble cast as a tool to create extremely complex and heavily layered stories.
One of the major advantages to using ensemble casts in television is that it allows the writers to create episodes which are centered around individual characters, using these episodes to develop the characters while also driving the plot forward. Lost, for example, famously uses this technique in combination with flash-forwards and flash-backs to provide more context for the incredibly complex Lost mythology, allowing viewers to get close to a wide assortment of characters.
In television, ensemble casts can save shows from becoming boring or repetitive. When a show focuses on a single star, viewers can start to get restless, and it can be hard to break out of a formulaic episode pattern. With this type of cast, the show tends to be much richer, with complex layers. For example, characters can be given opposing motivations, with centric episodes giving viewers an opportunity to sympathize with both sides.
Films may also use ensemble casts, which sometimes take the form of all-star casts, in which every member of the cast is a recognized star. Such casts can also add more depth to films; in the 2004 movie Crash, for example, a story is told from multiple perspectives, as viewers travel from one principal performer to another. Ensemble casts can make a film more dynamic, by providing an assortment of characters to focus on and emphasize with. Ensembles are also common in musicals, and they may be used in opera and other performances as well.
For producers, an ensemble cast can be a challenge as well as a pleasure to work with. Creating an ensemble generally drives the expense of a production up considerably, as stars who share billing expect roughly equal salaries and perks on the set. In television, where cast members can demand substantial sums for each episode, an ensemble cast can cause the cost of production to become stratospheric, and this becomes an even larger issue when big-name stars are involved.