killMAIL and Mailinator are 2 of, I think, many free online services that give you an instant, disposable email address. Great for use on websites which want your email address for apparently no reason other than to send you product updates, offers and other emails that you never want. Or you may be worried they will sell your email addresses to spammers. Or maybe there's that insurance agent who has been bugging you for your email address so that he can send you "more info".
Whatever your purposes and needs, I'm sure you'll find services like this useful from time to time.