Everything.
Don't you find it ironic that the people who pay for those subsidized A/C window units are prohibited from installing the exact same thing for themselves?
What makes more sense? Cooling a single room or an entire large house/apartment?
Whether the prohibition is by homeowners association, local, County, State or Federal law, it is a distinction without a difference.
From an energy standpoint, probably cooling the entire house/apartment with zone temperature control. Internal walls are not insulated so that if you attempt to cool just one room you are endlessly fighting the rest of the house. If you don't have zone control you can shut of vents to unused rooms.