I am a professionally trained home baker and own over 250 baking books. I also have a set of 16 binders I made for various products and projects while in baking school in the early 2000s along with a ring set of master formulas and a laminated 'cheat sheet'so I can bake any product, anywhere. In fact, I am in the process of writing my own book for like-minded home bakers incorporating many of the tricks and techniques I learned in the fabulous States-side Cordon Bleu-based program I attended (a two year curriculum - now that's thorough!).
So, I didn't need this book, but I was looking for a cookie book to give as a gift for my daughter -- who is a scientist and bakes on the fly -- that would present the standard variety (and hopefully more) in an accurate and easy to follow manner. None of the books I had on my own shelves fit all my criteria, so I did a little exploring on Amazon and found this one. I liked what I read enough to buy a copy for myself, first and have now given it as a gift to many people. I am very happy with it.
Once you know the ratios for each baking product [after all, the same four basic ingredients make up 95% of all baking: flour (base), water/liquid ('reagent'), eggs (leavening), butter/oil (fat)] what matters are the details and particulates added along with the proportions. In culinary school students memorize these ratios so they know the difference between a pancake and a crepe, a biscuit and a muffin. The trained eye can also recognize incorrect 'recipes' and wrong proportions that mean many bookstore baking books are useless and lead to failed projects (this is not a problem in Europe where formulas are considered sacred and product names reflect a standardized version of any baked product - almost as controlled as wines and cheeses! It is more of a dilemma here in the US where anyone can publish a book and call him or herself an expert - thus the dizzying and confusing array of baking books on the market here and their cumbersome size. Recipe books in Europe are concise - a small picture, a bullet list of ingredients, a short paragraph of instruction, since most people know what goes into making a classic croissant, for example and don't need or want every author to repeat it). For that reason, when I peruse baking books, I skip the measurements and instructions and instead merely look for interesting flavors, particulates, embellishments, i.e., the creative and imaginative input of other minds. For the accurate formula for any product, I turn to professional resources.
Now, having said all of that - back to the King Arthur Flour Cookie Companion. This is a great start for home bakers who want accuracy and a thorough range of standard US cookies without being burdened with too much technical information or formulas (recipes) that take too long to prepare. Most people do not have any time to waste. For a professional version of this kind of baking, turn to Wayne Gisslen's two introductory culinary textbooks (baking and cooking) - they are well worth the investment. Short of Gisslen, this book fits the needs of any home baker.
I am particularly impressed by the amount of professional instruction and explanation that they have managed to include without its interfering with getting the project done. There are simply shaded sidebars throughout that give the kind of tips that elevate the amateur product to the professional and commercial level. For example, using Fiori di Sicilia - standard in commercial kitchens, the principle of docking, without which many products will simply fail (pizza principal among them!) and dough relaxers, among others of this genre.
As for the issue that someone raised about the book failing to discuss proper ingredient temperatures, I believe this was done within the descriptions and explanations of the individual products - perhaps not emphasized as much as would be ideal, but again, too much technical information can be offputting to people who are not meticulous. The important thing is to have formulas that work even when today's hurried home bakers are a bit careless. This book provides those kinds of recipes. But, for example, the concept of eggs brought to room temperature is dealt with on page 485. Softened butter is discussed on page 484. Some cookies doughs need to be chilled and that is addressed throughout the book. Cold butter and cold eggs can be a problem when incorporating hot liquids or other hot ingredients but for the most part these are not serious issues when making cookies (in contrast, cold ingredients are key to a successful pie dough, for example).
Do not expect spectacular imagination and decoration from this basic, accurate, how-to instruction reference. You can find all of that in thousands of ordinary cookie books, online, most of them through Amazon. I still buy them from time to time, myself, to stimulate my own creativity.
There are a handful of professional baking books that the serious baker should have (Amendola, Gisslen, etc.). I keep them in one spot on my cookbook shelves. The rest of my baking books are just for their imaginative details - they are inspirational but little more. The reason baking seems daunting is that it is grounded in math, chemistry and biology. The challenge of all that is they are a bit difficult to master at first, but the reward is, once understood and properly employed, a correct knowledge of baking science will mean perfect outcomes, every single time and the ability to make one or a thousand items with rather simple equipment and tools, anywhere you land.
If I had to throw away all my famous-name, home baking cookie books and keep just one, it would be King Arthur's.