Forwarders create a simple way for creating email aliases. A great example would be if email@example.com wanted to get all email going to firstname.lastname@example.org as well. Through the forwarder interface, a website owner can do this in a few clicks.
The forwarder interface also allows the website owner to create a domain forwarder for all email that comes to their domain. Another great example is if email@example.com wants to receive all the email that comes into sample-two.tld. This allows the website owner to cut down on time spent checking email accounts.