Some websites may require more structural optimization than others. Like everything else in seo, it is relative to the needs of your website, as well as the competition you are going up against. For many website, you may need basic structural optimization such as putting links on your first page to a few focused sub-pages which provide relevant, targeted information.
For other websites, we may need to employ a more advanced multiple tier structural overhaul. Occasionally we use a siloing technique where your main domain links to a few different “silos”, or pages which are focused categories which have additional sub pages. These sub-pages also link to each other. Each category may need its own SEO campaign involving back-linking, and keyword optimization.