Having read that google likes sites that have sound or good linking structure I need to know what the heck that means. All of my pages are linked from my front page via section pages or subsection pages. Is that enough? Do I need to link from one subsection product page to another subsection product page? Is this going to help much on onpage seo or just a minor benefit or none at all?
One reason why interlinking within your site is great is because this makes it easier for search engines to follow links throughout all pages of your site more easily. Another reason is that Page Rank is attributed to pages, not sites. By linking to your pages from your other pages of the same site these pages are passing a bit of link juice to each other. Mind you, it's not as great as links from authority sites and maybe not as great as links from different domains, but it helps. When interlinking pages be sure to use keyword anchor text related to the page that you are linking to and make sure the content sounds natural. The context that the links are in (as in the text around them) is taken into account as well, so if you have irrelevant anchor text for the link and just put them in a random part of the page that is unrelated to the context of the page this will get noticed. In other words, make sure that your content is relevant and that the link is relevant within your content (and that the anchor text is relevant to the page you are linking to) and always keep user experience your top priority.
Inter-linking allows all of your content to be indexed, not just a few sniplets. For one, people used a variety of key word phrases to locate information in the SErp's. Many of my sites have pages that rank for different search terms, even though it's the same page. Links get your content found. If you create sub-content that steers away from your main-topic, create links to other quality on your site that compliments it.
If you want to understand how a well executed interlinking of pages can affect your rankings in the search engines, read my response to a post yesterday about silo or pyramid theme linking and how it affects renkings.