Most of the time, you don’t have to pay attention to the pressure gauge of a machine. But if you are having problems pulling a single shot, this can be one place to look to diagnose potential issues.
The portafilter locks the grounds into the espresso machine group head. The group head is the last place the water reaches in the machine before making contact with the coffee bed.
Though this piece isn’t attached to the espresso machine, it is vital to tamp coffee flat into the portafilter evenly and safely.