An XML sitemap is a list of your website’s URLs. An XML sitemap acts as a roadmap, which tells search engines what content is available on your website and where to reach it via its URL.
It’s more time consuming for a search engine to “crawl” a website and has to go through (in some instances) several pages before it finds the content it was looking for. An XML sitemap means that a search engine only has to read one page and assist search engine “crawlers” to index pages much faster. This is especially useful for deep websites with thousands of pages, frequently added pages and frequently update content too.