XML Sitemap is a machine-readable file listing important URLs that site owners want search engines to discover.
It matters because technical issues can prevent great content from being discovered, rendered, indexed, or trusted. Strong technical foundations protect rankings during redesigns, migrations, content expansion, and platform changes.
Example
Example: After publishing 200 glossary posts, an XML sitemap helps search engines discover the new URLs. It does not guarantee indexing, but it improves discovery and monitoring.