A few months back I flew CO ATL-EWR with my wife. We had 3 pieces of luggage. We used the automatic check-in machines, but when we went to give in the luggage we were told that I had been selected to have my bags searched. I had been selected, not my wife. So they asked me which bag/s was mine!!! It felt so silly. It means that if there was something illegal or dangerous in one of bags I could have simply said that a different bag was "mine". And they would have of course only checked that one, because my wife wasn't selected and the other ones are "hers".
Tip to smugglers- travel in pairs; make sure all the good stuff is in one bag.