Content and scope
Songs included on a compilation album may be previously released or unreleased, usually from several separate recordings by either one or several performers. If by one artist, then generally the tracks were not originally intended for release together as a single work, but may be collected together as a greatest hits album or box set. Compilation albums may employ traditional product bundling strategies.
According to sound technician Richard King, classical music compilations "may require more processing to match tracks coming from various sources and recording venues as well as the different sizes of ensembles."
In Christgau's Record Guide: Rock Albums of the Seventies (1981), Robert Christgau said, "While compilation albums by album artists (as opposed to stylistically unified singles specialists) are often useless, sometimes they present themselves as events", citing as examples the 1971 Ray Charles LP A 25th Anniversary in Show Business Salute to Ray Charles, The Kink Kronikles (1972), and Changesonebowie (1976).