You can certainly have one down comforter for all seasons as the choice of a down comforter should be based on the temperature of your room. Even in the warmest climates a down comforter with the right weight can be used due to the need for air conditioning. Some people like to have a fall/winter comforter so they can have the puffiest look and maximum warmth without turning up the thermostat. Then they have a spring/summer comforter or a down blanket which allows for less air conditioning. If storing a winter down comforter, it is important to store it in an all cotton bag which we can make. If the down comforter is not due for a cleaning or renovation, air it out on the clothes line on a dry, warm day so it goes away refreshed, ready for fall.
The spring and summer is of course the ideal time to send in your downs for cleaning and or renovation (cleaning and new cover). Be fall ready and avoid the rush by sending your down comforters, down pillows, featherbeds and toppers in early.