PID is an important feature for rancilio machines because it allows users to more precisely control the espresso brewing process. By monitoring and adjusting the pressure, temperature, and flow rate of water during the espresso brewing process, users can ensure that their espresso is extracted perfectly every time. This results in consistently great-tasting espresso and fewer failed shots. PID controllers are common in industrial and commercial settings, but they are also becoming increasingly popular for home use as well. Many high-end espresso machines now come equipped with PID controllers, and there are even some aftermarket options available for those who want to upgrade their existing machine.