An XML sitemap is a file that lists all the pages on your site in a format search engines can read. It helps crawlers find and index your content efficiently, especially for larger sites.
The Simple XML Sitemap contrib module generates sitemaps automatically based on your content. Configure which content types and entities to include, and the module creates and updates the sitemap files as content changes.
Once generated, submit the sitemap URL to Google Search Console and Bing Webmaster Tools. The search engines will use it to guide their crawling. Large sites benefit most from sitemaps because they help ensure less linked pages still get discovered. Smaller sites get less benefit from sitemaps since search engines can crawl everything from the homepage, but generating one is still recommended as a best practice.