Radiator controls are used to control the temperature in individual rooms. Thermostatic radiator valves (TRVs) enable you to be more energy efficient, by preventing rooms from overheating. They allow you to set different temperatures in different rooms and also enable you to turn off the radiator in rooms that are not being used. All of these things help to reduce energy bills and increase comfort levels.
TRVs sense the air temperature around them and regulate the flow of water through the radiator that they are fitted to, to control the temperature in that individual room. They should be set to the desired temperature in each room and then left to do their job.