The taste and quality of any espresso coffee are influenced by the water's temperature running through the ground coffee beans.  With high-temperature water,  your espresso will taste bitter.   But if the temperature is too low,  you can have an acidic coffee cup that nobody wants to experience every morning.  A PID temperature controller allows you to adjust the temperature to get a delicious cup of coffee every time.  With this feature, you can also adjust the steam pressure within the unit.