when you try to set up something like that in google, you will see. it is quite inconvenient, to add an email address to the forwarding list, the person with the new address has to send back a confirmation password to you, than you have to set up new filter for forwarding, etc.
if you later want to add a new person, or remove someone, you have to again meddle with the settings.
for me it seems much cleaner to remove / add a person by simply removing / adding a line of code…
also, if in the future i have to implement something like that in one of my clients project, than i have no other solution just code, because most clients are not capable to set up souch forwarding in google or other mail.