- It enables you to edit or delete the message prior to it being read by the recipient, if you wish to do so, as long as it remains in your "Outbox"
You can know whether or not your message has been received and (presumably) read.
If you receive an e-mail notification that you have a new Private Message, only to find no PM in your Inbox, it probably means the sender deleted it before you accessed your PMs. The sender has that option as long as the message is in the sender's Outbox. E-mail notifications are sent immediately when the PM is submitted and cannot be taken back if the message is deleted afterward.
Finally, be careful when deleting PMs. If you click on the "Delete All" button and confirm the deletion, all your PMs will be deleted and cannot be retrieved. Be sure that's what you want to do when using that button. If you wish to delete only selected PMs, make sure you use the "Delete Marked" button and NOT the "Delete All" button.