If the air con is working fine then I would argue that a service is unnecessary. However, if the car is on a lease or PCP agreement, you should check that your agreement doesn't demand this maintenance as part of your legal contract.

The best way to keep your car's air con healthy is to keep it switched on. The heating system is designed to operate with the AC on 100 per cent of the time. If you switch it off for the winter months or long periods the seals may dry out and result in the refrigerant gas leaking. Switching off the AC for long periods will also increase the risk of the compressor seizing up.