Originally posted by winterwolf:
... if you already have your first email, why don't the person just continue using that first email. ...
Because that "first" eMail provider may not provide what the user actually needs for his general usage. Nevertheless, it can provide the user a starting point which allows him to set up another eMail provider that does provide what he needs thereafter. Many eMail services demand a confirmation e-address to start up their services, so a first-time user needs to start with a service that doesn't demand that (though they may want an address, phone number or cell number for confirmation).