Good as a backup

You can do your best travel planning using websites. Guidebooks are by nature outdated. On the other hand, if your phone dies or you don’t have WiFi handy, a paper guide book is essential. For Thailand, this book does a great job. It covers the major tourist locations and has mostly up-to-date information.

One thing specific to Thailand is the huge number of sleeping options. You do not need this book in order to find lodging, because you can quite easily find it either by searching a hostel website or asking a tourist agent on location. For most other things, such as food and tours and sights to see, this book covers them well.