I don't leave my aircon on all the time ( but it will be on all the time if you are using auto climate control though, even when outside temperature is less than the requested temperature - but all aircon is inhibited from running anyway if outside temp is below 4 deg C as there is a danger of evaporator freezing up). I use aircon as and when necessary - but I do turn it on at least once a week to keep the seals moving and the gas / lubricant flowing around the system. I have never had to replace a compressor or magnetic clutch on any Jazz I have had, ( had a magnetic clutch go on my Civic but by the look of the wear pattern on the plates the thing was a bad design to start with) - I think if you leave aircon on all the time something is bound to wear out / break sooner or later - but on the other hand if you leave it off all the time the gas will probably leak out and a danger of seals failing.
Depends really how many miles you cover, and how long you keep your cars, if you are a low miler or don't keep cars long you could probably leave it on all the time.... it does have a slight effect on MPG but nothing to worry about.
Thing I don't like about running it all the time in winter is that it switches both the engine and aircon fan on when it is running and they both blow cold air over the engine - which to me is not a good thing.
I certainly do not use aircon on longer journeys ( including climate control ) as when the air gets too dry in the car I get really bad sinuses and also a dry nose is more likely to catch cold or flu ( the mucus is in your nose for a good reason, it is your bodies defence against germs and pollen ).