This book covers in one chapter (Chapter 2) the standard LaTex interfaces for embedding graphic objects in a LaTex document. Most, if not all, of this material is covered identically in the authors' other book "The LaTex Companion" and even in the 15-year-old LaTex 'bible', "LaTex User's Guide and Reference Manual" by Lamport.
Virtually the entire remainder of the Graphics Companion is a one-by-one synopsis of various add-on packages for LaTex, and essentially all of this material can be obtained free by downloading docs for the respective packages from the internet. Further, many of the packages covered in the Graphics Companion involve the user writing raw Postscript, a curiously old-fashioned, or at least unnecessarily geeky, approach. Raw Postscript for graphics has largely been superseded by the use of software such as Matlab, Mathematica, Maple, and Mathtype that produce cut and pastable graphic output that can be inserted intact into a LaTex document with a simple \includegraphics command - about all the average current LaTex user needs to know from a graphics standpoint. I'm not familiar with the publication requirements of the research world outside of engineering and math, but I can't imagine that other disciplines haven't evolved similar tools with cut and paste graphical capabilities.
Huge sections of the Graphics Companion are devoted to MusixTex and various game description (chess, Sudoku, etc.) packages - choices that seem to have been made because (perhaps) there were available doc files that could be used (with permission) essentially intact.
So, although apparently extensively researched and competently written, the Graphics Companion seems to be not much more than a catalog and compendium of docs, and difficult to justify at the price. Some time spent on one of the LaTex forums will lead to at least as much useful information as this book.