[analog31]

Pretty much the same, adapted to the specific purposes. For instance, Nashville charts also include some notations for the form of a song, such as Intro, Verse, Chorus, etc.

A reason for the usefulness was how recorded music was made. The recording musicians had to be able to choose a key that accommodated the singer's range, on the spot. So a transpose-able format was ideal.

I think the industry in New York had a different scheme, which was to write for a "standard" male tenor voice, and rely on the musicians to handle exceptions.