The best feature of the Sitemaps service isn't really the sitemaps section, but rather the page that shows you what people are searching for when your site appears in the results, and how high you appear. It will also show you what they are searching for when they click you link. You could use this to determine how to improve your site if you are showing in the results but nobody is clicking your links.
I recommend Sitemaps only for new Non-established sites. Sitemaps help your Site pages to get indexed very quickly and start showing up deserved results within the Search. With sitemaps, you can get your page indexed within 2-3 days. I get my pages indexed within 3 days.