Linking to other pages in your website is important for a whole host of reasons.
Naturally, when a visitor reaches your portal, you want them to stay on your site and take in as much as they possibly can and by linking internally, you do away with the need of an unnecessary trip back to your home page every time.
Linking can also help your traffic statistics too and this will work favourably with the search engines. By keeping your bounce rate low you improve your number of hits and increase your ranking at the same time.