Final answer:
ActiveSync should be implemented when a mobile device needs to receive push email notifications.
Step-by-step explanation:
The ActiveSync setting should be implemented when a mobile device must be configured to receive push email notifications. ActiveSync is a mobile synchronization protocol that allows mobile devices to synchronize their email, calendar, and contact data with a Microsoft Exchange Server. It supports push email, which means that new emails are delivered to the device as soon as they arrive.