For using typekit, google fonts etc. But it's simpler to do web fonts manually in Twig templates/CSS.
D8 stable/mature - however it's confusing how you're meant to setup Typekit etc. and there are problems with uninstall it… (there was an old D7 "typekit" module - deprecated).
28 Aug 2018: can't be uninstalled cleanly. The method described in #24 here works: https://www.drupal.org/project/fontyourface/issues/2916712#comment-12751073 if for example, you get an "The "font" entity type does not exist." message when running drush cr