An XBRL or inline XBRL document references its taxonomy: schemas, linkbases and the schemas they import. While SkipExternalResources is true, the document loads only when every reference in that chain stays inside the document’s own folder, which requires converting from a path. A document that references a remote taxonomy, a file outside its folder or any file when loaded from a stream, or whose local chain is not well-formed XML, fails to load with InvalidLoadOptionsException. Nearly every published taxonomy is remote, so most filings need SkipExternalResources set to false.
WhitelistedResources is never consulted for XBRL: a whitelisted remote schema is still denied, because the schemas it imports cannot be judged without fetching it. Its entries are still validated.
With SkipExternalResources set to false, every taxonomy file the document needs is loaded, including schemas imported by remote schemas.