The Corsair XD5 reservoir + pump includes a temperature sensor which screws into one of the inlet ports. As my motherboard doesn't have a header I could plug it into and I wasn't interested in spending ~$100 on a Corsair Commander. So I just left it (along with the RGB connector) disconnected.
However, there are advantages to measuring the temperature of the water rather than components. One of the benefits of water cooling is the water has a very high thermal mass. This means the