Setting the policy to BlockLocalFonts (value 2) automatically denies the local fonts permission to sites by default. This will limit the ability of sites to see information about local fonts.
Setting the policy to AskLocalFonts (value 3) will prompt the user when the local fonts permission is requested by default. If users allow the permission, it will extend the ability of sites to see information about local fonts.
Leaving the policy unset means the default behavior applies which is to prompt the user, but users can change this setting