A really good explanation is here: http://www.quora.com/Whats-the-difference-between-fixed-width-ePUBs-and-PDFs http://www.quora.com/Whats-the-difference-betwee

A really good explanation is here: http://www.quora.com/Whats-the-difference-between-fixed-width-ePUBs-and-PDFs http://www.quora.com/Whats-the-difference-between-fixed-widt... but the tl;dr is: Different needs for different book types. Think of a reflowable epub as a .TXT file and a fixed-layout epub as an HTML file w/CSS. Yes, a .TXT file is indeed reflowable and adaptable for a screen size. But what if you're writing an instructional book? Or you've made an awesome photo book of your travels? This is where presentation is more important over reflowable. It's important that the images you are referring to in the text are on the same page. Fixed-layout doesn't have to mean exact pixel representations just as most modern-day web pages adapt to user screen size. You can still "reflow" your text into a fixed-layout epub, the creation tool helps make this easy. At the end of the day, the screen ratio of tablets is fairly similar, and epubs are just HTML + CSS. A fixed-layout epub gives the author the choice of control - they don't have to specify rigid container widths just as much as they don't have to specify a font.