An e-mail alias is actually an e-mail address that shares a mailbox with a totally different email. For instance, you can have email@example.com as well as firstname.lastname@example.org and emails sent to both of them will be received in one mailbox. This feature will make it a lot easier and more convenient to handle multiple email addresses as you will need to log in one single mailbox if you work with webmail as well as create one single e-mail address in an email app on your PC. If you create an alias, not only will you be able to receive e-mails, but you'll also be able to send out email messages from the various addresses and they'll share the Outbox, so you will have all communication in a single place. Using aliases is surely a replacement for making use of various e-mail addresses for several purposes or forwarding one address to another to be able to control the communication of both in one place.