This book is the standard that all hospitals use to asses the nutritional components of the diets the clinical nutrition manager writes. It is recognized by JCAHO as one of the 2 required nutritional analysis sources used for menus in the hospital's food service setting. Websites may offer nutritional information, but this is THE standard.
These days, calorie counts and nutritional information can be easily googled, however, I find this a nice handy kitchen source for those times when I don't want to go grab the computer.