When I review HTTP in my classes, I like to cover a bit of login analysis because an application may login for you and pass on your login credentials.
People are usually quite surprised when I show then how you might be able to see someone's HTTP login credentials.
Please note that this only works with certian types of authentication, but I always suggest you try it to see if it works. When this does work, it becomes a valuable troubleshooting technique.
In this video I show you how to use this Wireshark feature and decode my login credentials.