Many or those who switch to Adobe InDesign from QuarkXpress or PageMaker these days. Those who do might not need a book about everything that InDesign is and is able to do. What they need is a book about the differences in techniques between the applications. Then this book is a good choice. It compares how things were done in QuarkXpress or PageMaker to how it is done in InDesign. If you also want to dig a bit deeper into InDesign you buy both this book and Real World InDesign CS. If you only want to get started and get over the obstacles with changing to new application that in principle does what you have done for years in that other application, but in another way than what you are used to, you chose this book.
I warmly recommend this book, and I use it in courses for switchers to InDesign.