Setting the policy lets you set a list of URL patterns that specify sites that are allowed to access the user's high accuracy geolocation without first having to request the user's permission to do so.
Leaving the policy unset means DefaultGeolocationSetting applies for all sites, if it's set. If not, the user's personal setting applies.
For detailed information on valid url patterns, please see https://chromeenterprise.google/policies/url-patterns. Wildcards, *, are allowed.