The default behavior for installing fonts to a site's Font Library from a font collection is to upload the font, so that it is hosted on the site.

This may not be the desired behavior, depending on who hosts the remote font and what the site owner desires. Remote hosting with a CDN may be more performant for loading the font, but may also come with privacy concerns.

For the site, whether to host the font locally or host from the source should be configurable (via hooks, if not through the UI).

The provider of a font collection, when not bundling fonts for distribution in a plugin but hosting them on a server, may or may not want their server used as a font CDN, so should be able to specify if downloading the font to the site is required to use it.

More information about Font Collections, for context: #57980