A theater pipe organ is different from a classic organ. Classic organs have been used for centuries, mostly in churches. But in the 1920s, when silent films needed a large sound to accompany them, classic organs were re-designed to produce a new sound and the theater pipe organ was born.
The theater organ concert differs from an organ recital in that the theater organ artist usually introduces each number before playing it, developing a rapport with the audience. The theater organ artist is encouraged to put his or her personality into the performance.
The theater organ artist seldom uses sheet music. The artist orchestrates each composition by choosing which ranks of pipes will achieve the particular sound desired. A song will sound different when played by two different artists.
Source: Dickinson Theatre Organ Society