When you want two or more people to have identical privileges in a database, you can use an alias to make one user look like another to the server. For one login, you set up a user name and assign the appropriate privileges; for the other login, you set up an alias of the first user name. The result? Two people and two logins, but one user name and one set of privileges.
Setting up an alias can be useful when you want more than one person to have special privileges, such as the privileges of the database owner. The database owner can grant and revoke privileges from other users and can create new tables and views, but he or she can’t transfer the ability to grant these permissions to other users. Setting up an alias for special users to the database owner is the only way for the users to obtain this privilege.