While it is easy to malign Lab, and convert back and forth to RGB ten times to show how much damage it does to a file, it is a much more intuitive way to think about color and contrast. Even if you can do many of the color and contrast moves in Photoshop in RGB, it often helps to think about things in terms of Lab and the relationships between Lab and RGB. Read the book and take a way from it what you will. It is not the end all be all for everyday workflow, but it helps one to understand color and contrast.
If you are reading his most recent book, Lab aside, it emphasizes working quickly. Very quickly. In a methodical way. Many times I think one can get several minutes into editing a single image and lose perspective. In contrast, the idea in the most recent Margulis book is to work quickly and decisively, making several versions of a image and thinking about what works and what does not - often the final image is a blend the best of the results. In spite of what one might think, much of the book is dedicated to RGB and enhancing contrast in the RGB channels. This requires one to subscribe to the methodology espoused in the book, but even if you do not, you gain a much better understanding of how RGB channels capture and contain pertinent scene information for various types of scene lighting and content. Again, it makes you think about the image and its foundation, instead of simply sliding a contrast and clarity slider around.
This is nothing novel, per se, about these image editing elements, but they are worth considering - especially when applications, like Lightroom, do much of the thinking for you and are self-contained editing and printing environments that encourage conforming to their structure and sliding sliders ad nauseum. While it is interesting that Lightroom provides a method to make virtual copies of an image, ostensibly promoting variation, there is no way to combine these variations.
And, as I'm sure you have already realized, just go to the curves window display options to change from Light to ink% to switch the direction of the curve axes, if that makes it easier to follow the book.
kirk