A PID controlled espresso machine like the Breville BES840XL will regulate the temperature in calculated steps until it has reached the perfect temperature.
Without a PID, only a mechanical thermostat regulates the boiler. The consequence may be an unstable temperature balance which could negatively affect the taste of the espresso.
What Is Pre-Infusion And Does It Matter?
Pre-Infusion is a set wait time where some water is added to the packed grounds before the regular pump process under full pressure is started.
This may positively affect the taste of the espresso since all grounds are equally saturated which results in an even brew extraction. So in my opinion, yes it matters!
Dry Puck With 3-Way Solenoid Valve
Both the Breville BES840XL and the Gaggia 14101 Classic are equipped with a 3-way solenoid valve which releases the water pressure off the portafilter and bypasses it into the drip tray after the brewing cycle. The result is a dry coffee puck that leaves an almost clean portafilter after dumping the grounds.
In addition, the valve closes automatically after the brewing process to eliminate the bothersome dripping through the brew group.