Why 2 temp sensors

[B5NUT]

I'm sure this is a simple one but why are there two temperature sensors on later model B5's? I did the one behind the engine last week due to a problem with the instrument cluster temp not working correctly, however this evening I was told the best way to drain the coolant was to remove the bottom sensor, so that the hell is that sensor for. Also is it best to chuck the rubbish plastic clip in the bin and go for metal?

 

[aragorn]

The sensor on the cylinder head is an actual sensor (well 2 sensors), one which provides a temperature value to the ECU and one for the dashboard.

The thing in the radiator bottom hose is a pair of switches, one which activates at 95c and one which activates at 100c (i think). These are used to control the auxiliary cooling fans two speeds.