This book takes a look at the process involved in maintaining the CSS for high traffic websites, when working in a team environment. It focuses on a few key areas, performance, frameworks, devices, accessibility, testing and debugging as well as the tools and processes you can use to make working in a team environment more productive.
Pro CSS for High Traffic Websites is a book aimed squarely at developers working in a team environment. If you are part of a team that maintains the CSS for a large website, and you want to improve the processes your team uses, then this may be the book for you.
On the other hand, if you are building a small personal site and trying to learn some CSS, then find another CSS book.