I had hoped to get some ideas on how to manage the documentation process for the handbooks of a software that is developed using agile processes. However, this is not what this book is about as it clearly states in its foreword. Instead it focuses on principles (or patterns) for project documentation in the development teams.
The book is structured clearly and it's easy to identify sections of interest and skip the rest.
I don't think it is a must-have book, but it gives some good ideas how to concentrate on the important things for development documentation.