Email aliasing is essentially when you give one email address more than one name. For example, you can add sales, info, and support as an alias to the joe@yourdomain email address and any email sent to sales@yourdomain, infor@yourdomain, support@yourdomain, and joe@yourdomain would be delivered directly to the joe@yourdomain email box. Only the physical or original email box (joe in this case) would need to be checked.
Probably the biggest advantages to email aliases are that there is no maintenance. The email is not stored in a separate location as they can be with forwards, so the maintenance is fairly simple.