In the XML sitemap , it is possible to add information such as Lastmod (last update date), Changefreq (update frequency), Priority (page importance) to the URL and send it, and Google will use this information as a reference for crawling.
In addition to the above, it is also possible to add video information to videos and image information to images (playback time, age restrictions, etc.).
XML sitemaps are mainly used to notify Google of URLs when large-scale sites are used, and when lower-layer pages are difficult to index ( internal links are difficult to reach).
Google also recommends using it for small external links, etc. if there are very large sites or pages where internal links are difficult to reach.