A few years ago I had the pleasure of working on an album by The Sounds of Blackness. They came over to perform at the Royal Festival Hall as part of the London Jazz Festival. They performed as a 16 piece on that stage, but are, on their biggest gigs a 60 piece outfit.
We had to set up a TV appearance and a live radio show while they were here. I asked Gary Hines, their MD (and a fabulous human being) what they could do. He showed me his carry on bag that accompanied hime everywhere. In it he had backing tracks so they could perform from 4 singers up to 30+. He also had the tracks on CD, DAT and standard cassette.
As @Beedster says, it depends on genre. It certainly worked very well in this case.