You might not need this book right now but if you have applications that use SQL databases then there will eventually come a day when you need the information from this book.
Any application that accesses a database will eventually present you with queries that run much slower than is desirable. This book provides you with a guide to how to resolve such problems and get your database accesses to run faster.
The most often suggested solutions are not always the correct ones and this book clearly demonstrates several situations where doing what appears to be an obvious fix (such as adding an index) may actually make things worse.
The author of this book has an in-depth understanding of how databases really work and as a result of the explanations that are provided in this book you can leverage on that to improve the performance of your SQL without needing as complete an understanding as the author has. If anything the book will actually help to give you a greater understanding of how databases work.
Are you going to know where to look when you next have a program that accesses a database starts running really slow? If you have this book in your library you certainly will.