ALMOST NOBODY GETS XML SITEMAPS RIGHT

Summary from the TLDR Marketing newsletter

XML sitemaps tell search engines which URLs a site wants in search results. They should contain canonical, working URLs that the site wants indexed. Google attempts to crawl each URL as listed, so redirects, errors, noindex pages, or conflicting canonicals make the sitemap less useful and can waste crawl activity. Missing or repeated ‘lastmod' dates can be acceptable. Fields like ‘priority' and ‘changefreq' are ignored by Google.