People absorb information in a variety of ways – auditory, visual, kinesthetic – so you need to provide them with the opportunity to take in your ebook content in more than one way. Some people will read it on their computer screen, others will print it out, and some will not want to read it at all. These people may want to listen to it on a CD in their car or as an mp3 file they can load onto their portable player.
The idea to to allow your audience to consume your information in the way that is most convenient to them. Give them more than one way to access your ebook and they will be more likely to purchase from you.