For full release notes, see: https://www.drupal.org/project/farm/releases/7.x-1.8
This release includes some Drupal core security updates, so it is recommended that you update as soon as possible. That said, they are mitigated by the fact that logins to farmOS are generally only given to trusted users.
This will be the last release of the 1.x branch of farmOS before the first beta release of farmOS 2.x! For more info see farmOS 2.x Releases (and What to Expect)