This is important because Google ranks web PAGES not just websites. There is no downside of having an XML Sitemap and having one can improve your SEO, so we highly recommend them.
An XML sitemap is a way for website owners to tell search engines about all the pages that exist on their website. XML sitemap will help you Onpage SEO your post and search engine bot will crawl your post faster and more easily
The Sitemaps protocol allows a webmaster to inform search engines about URLs on a website that are available for crawling. A Sitemap is an XML file that lists the URLs for a site
XML Sitemaps help search engine to find and classify your content which they have not find by themselves. They make it easy for google to find your site's page.
The Sitemaps convention enables a website admin to educate web search tools about URLs on a site that are accessible for creeping. A Sitemap is a XML document that rundowns the URLs for a site.