There are several good reasons to keep your vehicle air conditioning maintained and useable during the winter months as well as summer.
It is a good idea to operate automotive air conditioning systems periodically in winter to circulate the refrigerant around the system which also circulates the refrigeration system lubricants to protect and lubricate seals. Keeping things moving can prevent seizure of components such as air conditioning compressor and compressor clutch. Refrigerant leaks not only waste expensive refrigerants but may allow air to enter the ac system which can form moisture which then reacts with refrigeration lubricants producing corrosive acids and potential system component damage to compressor , pipework, and heat exchangers.
The air conditioning system can be used to dehumidify the vehicle interior to demist windscreens to keep glass clear aiding vision.
The air conditioning system dries the air inside the vehicle cabin by removing moisture and keeping blower vent ducts, seats and carpets drier to reduce chance of mould. Some people advise using the ac combined with the blower heater to maintain cabin temperature during winter.
Some climate control air conditioning systems have a heating function which can utilise refrigerant flow to be more effective than a traditional car heater system.
If an air conditioning system is leaking refrigerant then environmental pollution may occur. One may argue that running the air conditioner may require slighyly more engine power and hence fuel consumption and exhaust emissions but benefits often offset disadvantages if used in moderation.
Periodic change of the cabin pollen filter can reduce dust entry to vehicle interior.
Anti-bacterial treatment of air conditioner evaporator (heat exchanger in vehicle cabin) could be performed occassionally as part of a service schedule to reduce bacteria build up on heat exchanger fins where moisture has accumulated.
Periodic cleaning of air conditioning condenser (the heat exhanger often found in front of the radiator) fins can assist air flow through the radiator to maintain engine cooling. Heat transported from the vehicle interior is lost to exterior atmosphere from the condenser so keeping it clean allows better airflow and efficiency.
Air conditioner compressors are often driven by an auxilliary belt which may also drive alternator, water pump, power steering, etc, which should be checked as part of a routine maintenance schedule.