"Mutually Exclusive Transitions" is a property of all activities, but we recommend that you do not set this property directly. The exclusive gateway automatically sets this property to Yes.
This property, when set to Yes, declares that outbound links are mutually exclusive. This allows you to create loop-back links and create links that break out of a structured activity. Since there is no way to validate that two or more link conditions will not cause simultaneous execution of a target activity, you must set this property. For details, see
Process Developer Extension for Links
The Mutually Exclusive Transitions property is set to No as a default on all activities except the exclusive gateway, where it is set to Yes.