The user chosen as replacer can instantly see a new task in his mailbox …..

The assignment mail contains information to notify the user that he his someone’s delegate for this task. (But the previous participant is not notified).

In case of a notification mail - as opposed to an assignment– both the previous user and the delegate receive a mail.

The participants can clearly see if a user is a delegate or not, because a new column in the task summary indicates the replacements.