When you have registered a Gmail account, you become eligible to exploit all the services being offered by Google. One of the services being offered is the drawing the mails of your Gmail account from some other Gmail account. This means that if you have two Gmail accounts you can access account one from the other account without logging out again and again. By doing so, you thus save a lot of time. Most importantly once verified, you need not to provide your username and password for accessing that Gmail Inbox.