I was put off by some of the early reviewers of this book, who didn't find it as useful as they had hoped. And, perhaps partly because they had lowered my expectations--but mostly because of what I read in this book--I am overjoyed with what I found.
This book divides brewing into two parts: the brew day, which it calls the "hot side" (which it does not really cover), and what happens after you boil your wort, which it calls the "cold side." This is what the book focuses on. It's about yeast, sure: what they are, how they work, what happens to them under various conditions. But it's really about fermentation, this cold side: the way we control those various conditions to get yeast to do something we want them to do: make great beer.
And in its focus, White and Zainasheff hammer home the need for repeatability--same amount of yeast, same temperature, etc.
I think they are on to something. And if you suspect that your beer could stand some time and attention spent on this cold side of brewing, there is a wealth of knowledge here. For example, if you had to brew all your beers with just one yeast, what would it be? Two? Three? etc. How many yeast varieties should you try to maintain (based on how often you brew)?
This book treats the reader seriously. That means whether you are doing 5 gallons at a time with malt extract or running a microbrewery, the assumption is you want to make the best beer possible--and that fermentation control is key. I did have to smile at the chapter title "Your Own Yeast Lab Made Easy." And yet, for all the high-tech possibilities mentioned that might make your head spin and your wallet empty, there were many simple, free approaches to controlling and measuring your beer. And I think that chapter title captures the spirit of the book--first, to encourage you to think more scientifically about your beer (by which I mean "systemically," where you brew with intention)--which can be a bit off-putting if you think of yourself as a free spirit, creative type; second, that it is as "easy" as you want it to be. Take notes. Sniff. Taste. Do it again.
Do you need this book to brew award-winning beer? No. You just need a way to put the right amount of yeast in your wort and hold it at the right temperature(s) for the duration of fermentation--every time. If you are convinced, put this money toward a few flasks and a stir plate, a temperature controller, a fermentation chamber, and a way to heat or cool your beer as it ferments--and hold it to within 1 degree F of your target. But if you aren't convinced, this book might give you the information and knowledge, and allow you to benefit from the experience of these gentlemen.