I used this spread a lot in the beginning, it was the first "bigger" spread I was comfortable with. I really love the example she gives in the book, how two different courses of action give a different outcome; but I must say I never had such clear results with it myself. But it helped me understand that tarot does not predict the future, but tells you what will happen if you go on in this or that way.
I now don't use this spread so much anymore, but I have now learned to look at every spread I do as not what will certainly happen, but as a warning/advice: what will happen if you go on in the same way as you are at the moment (if you use a spread that does not show the underlying action explicitly), or in the way the cards are showing (depending on what spread you use).
So I can say this spread has been very useful to me