It is a fantastic "unabridged encyclopedia of all popular beverages" of that time. Broken down by liquor, this allowed a bartender to supply the order like an expert because he could reference it in this book under the bar.
Forget about bar bibles or encyclopedias, what about drinks that people really used? As so few bar books were written and even fewer survived at all from the past 100 years, it a great pleasure to be able to bring these drinks that were used at the time to our modern attention and use.