Nature: To move the feet and the body in rhythm with the music.
Optimum: When there is a strict correlation between the music and the movements of the body.
Usefulness: By participating, looking on, or listening with joy and accord.
Dangers: When the accord among the musical notes is lost.
Neutralization of the Dangers: When the accord among the musical notes is restored.
[The Tacuinum of Liege on "Sonare et Balare" (music and dance), f. 64v, as quoted in The Medieval Health Handbook: Tacuinum Sanitatis, by Luisa Cogliati Arano, translated and adapted to English by Oscar Ratti and Adele Westbrook.]
Note that this officially supports only doing Pump It Up numbers that actually look like they match the music, rather than some of the really sick upper-level Hard and Crazy songs that involve just moving as fast as possible while nearly arbitrary music plays.
It also assigns usefulness to watching someone else, so I do get exercise just standing there watching the really good guys making me look like a rank amature.