Other web sites will find it difficult to link to specific content on your page. This is the web, and webmasters want to link to pages on a site which pertain to their own content. If you have one long page, you effectively discourage this kind of linking, which means you will get fewer links. You are not creating a book which goes from front to back - you are creating a web of links from page to page. The really good webmasters learn how to take supreme advantage of this fact and create web sites that are a dream to navigate.
Pages flow from one to the other, with links here and there where appropriate.
Take advantage of hyperlinks and split a large document up into as many smaller documents as necessary. Link them together as appropriate.