Originally Posted by
Rawhide
Yup, there was, and it was awesome.
Joss Whedon had always want to produce a musical, and when he knew he had such a musical cast (Anthony Stewart Head was in a band as well as a West End production of The Rocky Horror Show (they even released him singing Sweet Transvestite as a single), James Marsters has played solo and in a band, Amber Benson didn't have such a musical background but happened to be quite good), he knew he just had to make a musical episode for Buffy. He was adamant though, that it can't be a once off standalone kind of thing, it must have a lasting impact on the plot (and that it did).