Jetpack Sitemaps make it easy for search engines to find your site and include it in relevant search results.
The Jetpack Sitemaps feature will automatically create sitemaps for you — a special type of file that search engines use to keep track of all the content on your site. This is not the same as a sitemap that users can visit to see all of the content on your site.
To enable this feature, go to: Jetpack Settings > Engagement and click on Sitemaps. Then, you can click to view the URL to your full sitemap, or to a sitemap of just your posts. If you’re submitting your site to services like Google Webmaster Tools, it will ask you for a sitemap.
It’s important to note that if you already have another plugin generating a sitemap, you will not want to enable both features.
But, if you’re submitting your site to search engines and you’re not already using another similar plugin (like Yoast SEO) you can enable the Jetpack Sitemaps feature to quickly get a sitemap for your site.