Originally Posted by MSPeconomist

The problem is that the bag is out of your control, so anything that you wouldn't put into a checked bag, such as medicine, electronics, jewelry, and other valuables, would need to be removed. If there's concern about the bag being mispaced--for example if it's taken from the passenger before the gate--then you would also need to place needed items for the first day or so at your destination into your smaller carry on piece. For many people, this would become almost as big of a nuisance as checking a bag.