This is a often talked about subject, and there are two schools of thought. The one that is prevailing is that it is healthy for your AC compressor to run. The coolant contains the lubricant for the compressor, and the idea is that when it is running, it is being lubricated and the seals won't dry out.
On 1996- MB AC systems, the AC compressor is a variable pressure system that runs the AC compressor all the time, regardless of ACC temp setting. It simply keeps the evaporator at about 3-4C, using the variable pressure system instead of cycling the compressor on and off. This seems to have increased the overall reliablity of the AC compressor.
On our old 1988 626 I would make sure I ran the compressor during the winter months (in heating mode for dehumidifying) and the AC system is just now requiring service 16 years into the car's life. And the compressor still works perfectly.
1998 C230 "Black Betty"