Sync Direction option is designed to specify in which direction should the calendar events / contacts / tasks be synced;
By default, Two-Way Sync is enabled for Calendar Events, Contacts and Tasks. Sync Direction can be set separately for calendar events, contacts and tasks.
For Calendar events additional sync direction can be set - "Free-Busy" sync to one side. When "Free-Busy" is enabled for calendar events, only the availability information will be synced to the specified side. Calendar event name, details, and most of other information will not sync.
You can currently set sync direction only if you have exactly 2 sources. If you want to set up custom sync direction scenario while having 3 or more synchronization sources, feel free to contact us.
Please note - if you enable one-way synchronization for calendar / contacts or tasks, and add 3rd or more sources, they will be added as one-way sync only to preserve your information.