If you would like Google to report on your Sitemap and notify you about the errors and index status of the pages in the Sitemap, click Yes. You will need to send them to Google Search Console (formerly Google Webmaster Tools). One of the items listed in the Search Console Help document under "Why my sitemap is not listed" explains this:
Only sitemaps submitted with this report will be listed. Sitemaps submitted using google.com/ping or robots.txt will not be included in the report, although Google can find and use them.
However, you do not necessarily need to submit your Sitemap to GSC for Google for easy retrieval and use. You could add one
Sitemap Directive in yours
robots.txt File. For example:
This will also inform other search engines, not just Google. However, this alone may not be as immediate as submitting your sitemap to GSC because it depends on yours
robots.txt File is being crawled. And as mentioned before, if you do not really submit to GSC, GSC will not recognize you and you will not benefit from Google's Sitemap reports.
Search engines are unlikely to retrieve the sitemap when it is simply uploaded to the document root directory. XML sitemap files can be called anything. So search engines do not necessarily know what to look for without being told. If you called it
sitemap.xml Then you might expect search engines to pick them up, but I do not see requests for that
sitemap.xml in my access logs (for sites that do not have an XML sitemap), this strongly suggests that this is not the case.
If your Sitemap changes, you'll need to retransmit it (or let Google know) that your Sitemap has changed. This can be done automatically pinging Google (a GET request) without manually resending the Sitemap. For more information, visit the Google Help Center to submit Sitemaps.