Using the "Is Primary" Relationship Setting

When a relationship is created, the option to Allow Primary for that relationship is available.

When this setting is enabled in the relationship type setup, when that relationship is used on a Customer Record, the "Primary" check-box is visible.

Primary Organizations Appearing on the Individual Record > Overview Tab

When the "Primary" check-box is selected for the organization during an "organization to individual" relationship assignation, this causes the organization flagged as primary to appear on the Overview tab of the Individual Record. Multiple organizations can be flagged as primary, as is evidenced in the image below.

Querying on "Is Primary"

The "Primary" check-box can also be included in queries by inserting the "Is Primary" field into the search.