Both sentences ask for clarification about why the book is helpful, but they have slightly different focuses: * Sentence ①: "Why is it helpful to you?" focuses more on the reason or cause behind why the book is helpful. * Sentence ②: "What's helpful about it to you?" shifts the focus to what specific aspects of the book are helpful, asking for more detail about the helpful features. So, while the general idea is the same (asking about why the book is helpful), the nuance of the question is a bit different.