If the subscription of contact changes then it will change the customer’s subscription status.
A user event is created for this. User event will compare the global subscription status of contact with the customer record which has the same email after the update of contact. If the subscription of the contact changes then the subscription of the customer with the same email also changes.
So whenever the Global subscription field and subscriptions of contact change and the record is submitted that change is also shown for the customer record which has the same email id.
