Having a lightweight reference for simple things that I only do occasionally is a godsend and a massive time saving. I can dive into Deployment from Scratch and tweak something that needs updating, or even deploy a new system in less time than it takes me to lookup and parse/refresh my knowledge from the actual documentation on most topics. And even if I do need to refer to the docs for something not in the book, it is much much quicker as I have the context already.