Apart from being fresher, the grind is also one of the ways you control the pressure you extract at in an espresso machine. Depending on the machine you can ei

Apart from being fresher, the grind is also one of the ways you control the pressure you extract at in an espresso machine. Depending on the machine you can either time the shots, use a pressure gauge or just look at the flow coming out and verify by taste. It's not much more complicated than if the pressure is too low the shot will taste sour. So you adjust the grinder to grind larger. If it's too low the shot will be overly bitter. So then you grind smaller. I'm told the ideal pressure is 9 bar but really taste is the real test. Once you have the grinder dialed in it will probably be fine for the entire batch of beans and only need tweaking when the next batch comes in. (Although if you may have to tweak it as the bag ages.)