Just as a matter of interest I desided to change my head gasket, P gasket and timing belt last month, and did'nt bother to replace the viscos fan, I drove it around town in traffic jams but the temp gauge didnt alter at all.
Then went on holiday to Devon done 900 miles 70 on the motorway a few hold ups, temp gauge as normal even after being sat for 20 mins with the engine on, sounds quieter and I think fuel consumtions gone up a bit cool engines these 300TDI's

This is a long standing bone of contention, I tried it, didnt like and put the fan back. Even when not doing much, it still keeps the engine bay cooler so it's still a good idea.

Some people swear by taking it off, some say put it back, I know which way I went