On March 6, we released a major update of our Yoast SEO plugin. This update was aimed at making SEO easier and more understandable for our users. We removed quite a few settings and options. In other cases, we changed the names of settings making them easier to understand for non-technical users. All in all, …Read: "Why we changed so many things in the 7.0 update"
In short, XML sitemaps are a list of URLs of a website. Apart from the URLs, they can provide additional data about a page, like when it was last updated, how often it’s get updated, if a page contains images etc.
XML sitemaps help search engines to crawl your website and find all important pages of your site. Usually crawlers simply follow links on your site to find all content. Implying that if your internal linking structure isn’t flawless, they might miss out on some content. This issue can be prevented with an XML sitemap. If you have an XML sitemap that lists all important URLs of your site, you ensure that crawlers will encounter these URLs.