Historically, many machines on campus have received email. You probably only want to read mail on one and don't want to miss messages sent to the wrong machine. You might not even have a login name on those machines. For many reasons, it is convenient to make email addresses that don't correspond to login names. Some of these are for groups of people and some are used to address people in certain roles.
Machines come and go.
Even big popular machines can get retired and then you won't get email there any more. If you printed your email address on your business cards, it'd be wrong after that machine went away and people couldn't find you. And you'd have to chuck your business cards and get a new batch. They aren't necessarily based on logins or host names. You can store the mail there and read it with a mail client, or you can forward it to your departmental account.