Hi Jeff,

In response to your question, "Or why not just use Jamey Abersold stuff?",
BIAB can be Aebersold that is created and manipulated by YOU.
You have total control of rhythm style, tempo, key etc, etc etc.
So if you want the Aebersold type backgrounds to play along with
BIAB will do the job.
Grab a fake book, select the tunes you want, input the chords and create
your own backgrounds.