This could be the most important Japanese grammar book you could buy, and I'll tell you why. If you're already learning Japanese, you know how complex the sentence structures and grammar can be. It's one thing to be able to get your ideas across in a reasonably intelligent manner, but it's another thing entirely to make what you're saying flow and sound natural. This book teaches you how to connect ideas and sentences so they more naturally flow into the next one. Now, if you're like me, you might be really good and saying things in Japanese, as long as you don't have to build on what you said the sentence before, or put together one long thought or sentence. This book shows you how to "look ahead" so you can figure out how to construct the sentence from the beginning so that, by the time you get to the end, everything has neatly connected itself along the way.
My only regret is I didn't find this book sooner than I did. It is truly invaluable for the beginning student, and even for the intermediate student, as well. Don't even hesitate to buy this book. It is cheap and EASILY worth the price.