If you can make your site with a logical and meaningful URL (web address) structure, all the better for search engine optimization (SEO).
A site's URL structure should be as simple as possible. Consider organizing your content so that URLs are constructed logically and in a manner that is most intelligible to humans (when possible, readable words rather than long ID numbers). For example, if you're searching for information about aviation, a URL like http://en.wikipedia.org/wiki/Aviation will help you decide whether to click that link. A URL like http://www.example.com/index.php?id_sezione=360&sid=3a5ebc944f41daa6f84…, is much less appealing to users.
Your site should have obvious major subsections, which search engines interpret from the folders (real or virtual) on your site. For example, UUA.org/beliefs shows that "Beliefs" is a major subsection of the Unitarian Universalist Association (UUA) website, and it may be shown as a "sitelink" if it's determined to be relevant to the searcher.
If following this advice would mean reorganizing your whole site, be sure to review this Checklist for Changing Your URL Structure.