I stopped updating my sitemaps a while ago. My information changes fairly often. I don't think it has hurt me at all as new content is being indexed very quickly (1-3 days average). My rankings have never been better. Does anyone know of a reason I should spend the time to update the sitemaps? Am I missing out on anything here?
I think , you have to update your sitemap whenever do update ur site, because crawler first read the site map.
The site map not only helps search engine index your site better, it's also part of security. You must have a robots file....and point it to the sitemap. That should direct most (respectful) robots to read your site via the sitemap and not go snooping around to find pages. But, also, lack of a sitemap does not and should not affect your indexing severely. Especial if you do proper linking between your pages.