It must first be mentioned that this is a book geared towards those with established photography businesses. Those just entering the business can still definitely benefit, but perhaps 50% of the reading will apply to a newcomer.
For those already in the industry, learning and refining your decisions is a huge part of putting value in your product and pushing you ahead of your competition. As such, this book is invaluable. From the range of topics it covers, it also covers them very well and in depth. This can be from how you handle clients, balancing family, pro bono work, effective e-mails, contracts or any other aspect of the business.
For anyone looking to improve or review what they do now and see if improvements are possible, this book is invaluable and a great reference to have near by.