For students: Unlike traditional course textbooks and ancillary materials, like homework systems, OER is completely free and students can access their course material on day one instead of waiting for financial aid or a paycheck. And, instead of selling the textbook, returning a rental textbook, and/or losing access to ancillary materials at the end of the semester, students retain access to OER for as long as it exists on the Web (or their computer, if they have saved it there). Also, OER is more likely to come in various formats (e.g. PDF, HTML, iBook, ePub, etc.), which lends a helping hand to accessibility.
For faculty: Research has shown that use of OER in the classroom can lead to similar or higher student success and retention as traditional textbooks. This may be because students have access to the textbook right away and students that would normally not be able to afford the course textbook, will now be able fully participate in class. The open licensing on these resources also allow for modification so faculty can remix chapters, change images, or alter in ways that work well for the course.