A quick 5 minutes to help you understand the importance of Book Design.
Book design comes down to the inside and outside (cover) and your reader's overall interaction with your book. If you make margins or use fonts that they aren’t used to reading, it can change the experience. Imagine if you watched a movie and someone changed the aspect ratio. Instead of it filling up the screen, it was off-center with black bars on the side. It would change your experience.
https://BHPubs.com