...
You can add portal users to a separate group or/and select a separate directory for them in case you’re willing to distinguish Communities users in your system.
Mail Notification
If checked Project Admins will be able to configure Portal notification for Communities and/or enable Jira standard notifications for the Communities project.
Anonymous portals
If checked Portal Admins can allow users to access Communities without having an account. Anonymous users can view Posts created by other users, attachments, current statuses and public comments. Anonymous users cannot add new Posts, comment, vote and search within the Portal.
Portals
List of projects for which Communities is enabled.