have you ever needed to access the same webmail using two different accounts? You can say "hey what heck are you talking about?". OK, here is the scenario, you are using your notebook and sundelly your girlfriend, brother, sister or any other person, wants to check his/her e-mails. Oh, wait! Both of you have account at the same webmail provider (e.g. Hotmail), then you have to log off from your account ir order to this other person access his/her account.
Despite the fact that you may writing an important e-mail or downloading some attachment, no problem.
Isn´t that upset? If you are using Internet Explorer 8, you don´t have to worry about this anymore. You just have to open a New Session and keep both sessions opened without loosing anything.
This also applies if you´re using OWA (Outlook Web Access) on a business travel and you have to share the computer with a collegue.
For more information, check this: Session Cookies, sessionStorage, and IE8 or “How can I log into two webmail accounts at the same time?”