The plugin loads the font(s) used in /wp-content/uploads and starts loading them from that directory, reducing the loading time drastically.
I ran into a bit of a problem by adding a ssl certificate to the site later, causing a mixed content error:
The page at ‘https://whatever.com/’ was loaded over HTTPS, but requested an insecure font ‘http://whatever.com/wp-content/uploads/2019/04/ahcfv8qz1zt6hCC5G4F_P4ASpU8-3.woff’. This request has been blocked; the content must be served over HTTPS.
Adding an ssl certificate after installing WordPress does not update /wp-admin/options-general.php 😉
After Danny pointed that out, only a rather persistent cache got in the way temporarily. All is fine now!