This explanation seems to be lost in the current README
You’re asking: "why would I want multiple sessions?". Take this example:
You have an app where users login and then need to re-login to view / change their billing information. Similar to how Apple’s me.com works. What you could do is have the user login with their normal session, then have an entirely new session that represents their "secure" session. But wait, this is 2 users sessions. No problem:
# regular user session
@user_session = UserSession.new
@user_session.id