The leads are moved into the "Exhausted" status once they have recieved any availble content within a stream and have not transitioned into a different stream. It is done automatically. You do not need to create a Smart Campaign to do this.
I'm not 100% certain in regards to your reporting questions, others should chime in... But I am pretty sure a lead being exhausted does not affect your reporiting on engagement. As far as I know, exhausted leads are put into a kind of holding pattern until they either move to a new stream or new content is added to the stream that they are in. It also serves as a reminder notification for you, so you know how many leads are almost at the end of your stream in its current state.