Most web services, when you setup a new account, require you to provide an existing email address, for backdoor access. After you finish providing all of your personal details, and hit "Create my account" or whatever, you'll then see Check your email now, and reply to the message from us, so we can activate your account! You open your email, reply to the message or click on a link in the email, and you then see Congratulations, and welcome to our service! By verifying your email address, you're ensuring that, one day when you forget your password, you simply click on a link "I forgot my password!", and they email you a hint, or maybe let you reset the password from a link in the email. Since you verified the email address originally, you know that you will be getting the "forgot password" email in your inbox.