Since musical notation only incompletely expresses the form of music, there is a whole continuum of possibilities concerning how much the performer determines the final form of the rendered work. Music composed in the Baroque era, particularly in slow tempos, often was composed in bare outline, with the expectation that the performer would ornament the work heavily in performance. Such freedom diminished in later eras, reflected in the increased use by composers of detailed notation, including marks of expression telling the performer more precisely how the work should be executed. A culture eventually developed whereby faithfulness to the composer's written intention came to be highly valued (see, for example, Urtext edition). This musical culture is almost certainly related to the high esteem (bordering on veneration) in which the leading classical composers are often held by performers.
The historically informed performance movement has revived to some extent the possibility of the performer elaborating in a serious way the music as given in the score; this however might be considered a way of creating greater faithfulness to the original in work composed at a time that expected performers to improvise.
In genres other than classical music, the performer generally has more freedom; thus for instance when a performer of Western popular music creates a "cover" of an earlier song, there is little expectation of exact rendition of the original; nor is exact faithfulness highly valued.