I suppose, although I'm no aficionado, it's a catch all, umbrella term for country, bluegrass, blues, jazz, etc without having the snobby "that's New Orleans Jazz not Appalachian Mountain Bluegrass" catagorising.
One of the bands I play in does Mod(60s & rivival), Ska(1st & 2nd wave) and Northern Soul, there is also a crossover from punk where ska was prevalent. We could do with a similar catch all term as I usually just say "the Mod band" but you can get the odd '"The Clash aren't Mod", or similar comments.
Unfortunately, catagories are annoying and useful in equal quantities.