I think the point is to use it as a dictionary. You read some Japanese out in the wild and come across some word or conjugation you don’t understand or have forgotten. You then proceed to look it up in the dictionary.
However, when I was going through Genki, I looked up every grammar point in the dictionary because the explanations are much better and more in depth.
I highly recommend this book to anyone who is serious about Japanese. For each grammar point, they explain how and when to use it, give multiple example sentences, list some additional notes to help you use it correctly, and explains how some other grammar points are related to the current one.