Can you please define Active User Sessions as in "There are 53 active user sessions right now."

Also define and explain benefits of Registered Users.

Sure.

Active User Sessions: That's the # of people currently browsing through the forums, whether they're logged into the forums or not.

Registered Users Online: This is the # of people currently reading the forums who are logged in. There is no particular benefit to being logged in unless you want to post a new topic or respond to an existing topic. You have to be logged in to participate.

Both of these numbers are really just for fun -- they're there to give you a sense of how many people are currently participating in the various discussions taking place here.