When I did a chip tune to my car I heard the engine cooling fans come on for the first and only time.

Should I be concerned that I haven't had that experience after normal driving?

My C4S fans came on just about every time I turned the car off!

 

My 997.1tt was similar to your C4S... fans came on after pretty much every drive. I've never heard them come on after shutting my .2tt off.

 

The fan is not to cool the engine down, it's to keep the ancillaries that are on top of the engine cool (e.g., power steering pump and etc.) by suckingin the outside air. It should come on after you turn the car off, definitely if the car came up to operating temperature. It may take a few minutes after the car is stopped before it turns on and it may turn on multiple times, but it has to turn on. If not, something is wrong.