Thermostatic Mixers helps maintain a certain water temperature (of your choice) throughout the duration your shower. It helps to prevent sudden changes in the water temperature to ensure you will not burn yourself. This helps to protect kids or elderly from getting scalded by sudden water temperature change.
It is also convenient as the mixer will maintain the selected temperature throughout the shower even if you stop the water in the middle of the shower. This will let you enjoy your shower without worrying about the change of temperature in the water.