Sitemaps offer a number of advantages:
• They can serve as a navigation aid for your website visitors.
• They help improve search engine ranking by helping search engines find and index your pages.
• They can contain your most important keyword phrases in your link text, to help your web pages rank higher for those terms.
To help in creating and updating sitemaps, I like and use GSiteCrawler for Windows, at
http://GSiteCrawler.com
It has multiple handy features and is free (although the author appreciates modest donations for his work and there's a nag screen to remind you of that).