This feature allows dynamic share to limit the fields that are being shared on referenced records. After clicking “Share only selected fields” on a given referenced field, clicking the “Add new” would specify a field to be shared, and clicking “Add all table fields” would share all fields of the given record.
Example: This dynamic share on the “Ticket” table is configured to share out the “assignment_group” field. The “assignment_group” record is configured to share out only a few fields - 'name', 'manager', and 'roles'.
When a dynamic share is triggered, the “assignment_group” record will only have the three fields selected to be shared.