Webmail Login:
It is quite possible and often the case that there is more than one email account for your domain. This is why we provide separate and individual email login for each pop / imap account.
Control Panel Login:
Access here relates specifically to settings for your domain name. As you may have more than one product or domain, you will require access for each one. Furthermore, you may wish to provide selective access to your web developer.
Billing Account login:
Account / billing related information is provided solely to the account owner. Therefore a separate account login is required. Your username is simply your account no. published on every invoice. Similarly once the owner is logged in the can also generate support tickets which are encrypted for added security.