Although its not listed in the manual, running water through the brew group and empty portafilter before brewing is a great idea. This helps to ensure that all of the external components of your espresso machine are at the proper temperature for a great extraction (and you can dispense the water into your demitasse cup to pre-heat that at the same time!). We generally refer to this as a "blank shot", but it is also commonly known as a "cooling flush" - specifically when youre running the blank shot after machine has been sitting on but idle for some time. If youre pulling back-to-back shots, its not something you need to worry about. As stated, its simply a tool to ensure the portafilter and group head are at the proper temperature before brewing.