Well if you, like me, want to provide your readers with a wide breadth of options that suit reading preferences (online/Print) or even if you want to provide a basic documentation set, you still need to provide a help to go inside the product and a PDF to accommodate the people who like to print the manual. I add to that an online information center which is basically the help published to the website so that search engines like Google can find specific content and present it in a less intimidated format than a long PDF file.