It's not just lost luggage. My trip to Rome last month was SFO-LAX-ORD-LHR-FCO. I know, not the best route, but a great first class fare. LAX-ORD had a mechanical delay that kept getting extended. Finally, it became apparent that I would miss my ORD-LHR flight. So I went to the Admirals Club to request a reroute. They asked if I had any checked baggage. I said no. They switched me to a direct LAX-LHR flight, which was sweet. A nice long flight, with an opportunity for a lengthy sleep. That would not have been permissible with a checked bag. I would have wasted a day, and missed a wonderful event that I wanted to attend.