IMO, one hardly needs back door auto windows, why, because if we drive with open window front and back, it will allow air to pass across whole car, this is not a pleasant thing in jammed packed traffic since there will be lot of smoke coming in. It is not feasible either on free roads as high pressure wind will create noise as well as take dirt into the car, not to forget your hair style will be all ruined too.
However front windows are important, specially when you want to swear someone for bad driving :p, at petrol pumps while payment etc. I always drive with back windows fully up, If with family i always use AC, in winters i just adjust the thermostat. While driving alone in winters i partially pull down my window, so it will not create suffocation and it is better to get one window down instead 2 because if one window is down air will not pass across the car so interior is safe so as your hairs and lungs if you know what i mean :).