This is why Jeff's courses are so cheap...or so darn expensive. Either less or more than the number of holes required.
One of the best descriptions is from Bill Amick: "It is something that goes out and comes back, what more does one need to know?" That was his wit upon hearing that a publisher had actually offered to print and distribute a volume on the subject.
Another decent observation: "Routing is something that most people cannot get in their head all at one time...most people have ability only to think of golf holes one at a time." — Desmond Muirhead.