"The Practice of System and Network Administration" is different from most of the other technical books on a professional SA's bookshelf. This book is about how to become a professional system administrator.
The profession is about more than knowning obscure options to different commands. To become a professional, a system administrator needs to change mindset from a straight-ahead techie to a member of the team who has specialized expertise.
System administration has not always been recognized as a profession. System administrators themselves are partly to blame for that. We have tended to focus strictly on technology and not on how to structure our work to benefit both ourselves and the organizations we work for. Limoncelli, Hogan and Chalup have put togeter a great standard reference for people who are ready to transition to being professional system administrators.