Are we talking fully automated ship with no crew? What would be the point of that? that's basically a space probe, and a space probe can be built MUCH smaller than any ship.
Or a combat drone.
Two of the three parts of the Prometheus were effectively drones, and you can even say that the whole thing was (since it was de-crewed) given that the two EMH's were simply computer programs.
TAS shows automated freighters as nothing out of the ordinary, so it would seem normal that in peacetime, scheduled freight runs may often have been made by unmanned ships. Only unusual runs, or ships that needed to cross customs borders would need to be crewed.