A couple of people have commented to me that it is wise to run the aircon occasionally even if you don't need it. A few minutes every couple of weeks was suggested.
Being new to vehicle aircon I don't know whether this is dubious folklore.
However, using the aircon (which dries the air as a consequence of cooling it) for initial de-misting before the heating system has warmed up does seem an effective solution. - (#1545) Dave Mason, 3 Dec 01

Very important to use the aircon during the winter, otherwise the various seals in the system will dry up , with the attendant loss of gas.
And yes, demisting is a lot faster with the aircon on... - (#1547) david miller, 3 Dec 01