Can confirm. Reason:
The grinder will have a hopper on top. Typically you're going to open a sealed package of roasted beans, and empty them in there. It might then take you hours/days/weeks to go through the beans, depending on how many shots you are pouring a day. The hopper has a lid, but is by no means air-tight. So the beans will age/oxidize/deteriorate as they sit in the hopper, which changes their characteristics, and you'll usually be nudging the grinder occasionally to compensate. Ditto with humidity.
At my last job, we had a professional espresso setup right in the office. Each new staffer who was interested would go through an initiation, and various people around the office developed reputations for being able to produce coffees ranging from excellent to crap :-)
We had a grinder like this one, you'd find it in any café: http://www.mazzer.com/en/grinder-dosers/super-jolly/
Our coffee machine itself had two group-heads and an enormous brass boiler, and was plumbed into the water main. I do miss it.
Anyway once you've tamped and poured a few shots, you begin to get a sense of whether a given pour is too fast, too slow, or just right. Assuming you have a consistent tamping technique, it's the grind that's going to determine this.
Incidentally the grinder adjustments are super fine, the tiniest bump will change the pour noticeably. Coarser grind is going to give a faster pour, finer grind will be slower.