Your book will be much more widely available because it is online and free. OTexts enables you to reach a big audience. We have found that even when a print book is a prescribed text for a course, students will go online and look for high quality online alternatives.
In addition, an electronic platform gives you much more flexibility. You can have dynamic content (e.g, movies), interaction with readers via online comments and an online forum. You can update the book whenever you find errors, or wish to add more material -- you don't have to wait a year or two until the next print edition comes out.