I had been using Tableau for a while, and was figuring things out as I went along using the internet and trial and error, before I read the book. I got it in the hope that it would help me understand Tableau more completely, and assure myself that I wasn't missing any important capabilities, and I think the book did a good job at that. However, much of the information was already familiar (especially the information on what to click or which menu a command is in), so if you're brand new to Tableau this would be great, but if you are already a user, even if not a power user, then you'll find less here that's useful. Also, the areas are not developed in any great depth. For example, the writing of queries is discussed by general examples, rather than by principles.
The example workbooks are useful, and allow you to learn some useful approaches.
The book is also well written and illustrated.
So, the newer you are to Tableau the more you'll get out of this book.