Kindle Previewer is a preview tool for publishers to preview the layout of their ebook for Kindle devices. It's a great way for publishers to make sure their ebook is formatted correctly for devices that use the Kindle app.
Since Kindle is supported beyond Amazon's Kindle hardware and on other devices, it is important to make sure you are not releasing improperly formatted ebooks. Kindle Previewer will allow you to do this.
If you plan to release ebooks for Kindle, Kindle Previewer is a must-have program.