What is the importance of the Champagne Supper Club in the novel, On the Rooftop?

The Champagne Supper Club is a jazz bar located in the Fillmore neighborhood of San Francisco. This is one of the novel's primary settings. The Salvations have a deal with Mr. Bailey. They perform at the club on regular Thursday or Friday evenings. This is one of the primary venues where the sisters begin to develop their act together.