The sitemap lists all the URLs of your website. It is written in XML (Extensible Markup Language), which makes it readable for search engines. The sitemap helps search engines crawl your website and gives you the opportunity to prioritize certain URLs in the crawling process. The sitemap may also include additional information in its metadata, such as last change date of an URL, for example.
The value of the sitemap is sometimes overlooked. Though it doesn’t guarantee that all listed URLs will be crawled by a search engine, it nonetheless allows you to optimize and “guide” the crawling process.
Although a Sitemap.xml is a good way to optimize the crawling of the Googlebot, you should know that it does not guarantee that your submitted URLs will be crawled and indexed. Nevertheless, you should take the opportunity to increase the chance of crawling with a functioning sitemap.