Nah my knickers were in a minor knot because I thought the implication was that the only benefit of leaving cities undefended was the few gold saved in maintenance and therefore not worth doing . As you say , unit maintenance is not really an issue outside of the early game . In actual fact ( and I hate to pull out the "at high levels" chestnut) , squeezing everything you can out of limited resources is vital . Undefended cities ( especially behind the great wall) provides a significant advantage over the AI . In the early game , garrisons cost workers , granaries etc . Mid to late game with a large empire , the advantage of undefended cities can easily be another 10 units in your SOD .