Interesting, yes. Helpful to me as a photographer, only somewhat.
Smith presents a wide range of captivating portraits, each with a little background, and many with an anecdote or personal observation. The book is well organized; the information is clearly presented; and the explanations are typically bite-sized, not too detailed. It all makes for interesting reading (and observing), which I enjoyed.
Regarding helpful, my reaction is more mixed. As an amateur photographer, I learned (or re-learned) some useful insights into portrait photography--preparing in advance, building rapport with the subject, selecting lighting, choosing a lens--but many of Smith's experiences are totally foreign to me. As a no-assistant photographer, I never "weigh whether one assistant is enough or if two or three will make the shoot go more smoothly." Nor do I work with "hair, makeup, and wardrobe stylists," and I don't have a production van or provide catering.
So it's all very interesting, but not so applicable to my daily life snapping a few photos.