The primary reason to have links to internal pages is to help search engines locate your content and promote it's rankings. If you only link to your home page your PA of your more important pages will suffer.
Let's assume you sell various products and one of them is Nike WingedFoot sneakers. You provide the page as one of the 5000 products you offer and do not have links to the page. One of your competitors writes a fantastic article on how this pair of sneakers is the best thing and can make you jump higher, run faster, etc. He obtains links directly to this page. All things being equal, he will outrank you. Even without writing the great article if he gets the links and everything else is equal, he will outrank you for any similar search.
EDIT: I was ninja'd on the response by "the other Ryan". We are in agreement but worded things a bit differently.