Essentially, any restaurant that serves alcohol has to make the drinks in a "separate space" from where the patrons are seated, because innocent Utah souls should be protected from witnessing the devilish rituals that make vodka bearable to drink. Thus, many places have a sort of separate area in the bar, surrounded by curtains or frosted glass or well-trained guard elephants, where bartenders mix their drinks. We're not sure why the booze needs a privacy screen, but maybe slushing two drinks together is a bit too close to alcoholic premarital sex for Mormon tastes.
It's basically a glory hole for booze.
After what we assume was lots of campaigning and laughter from the citizens of Utah, the state finally passed a law this March to "remove" the Zion Curtain requirement, though what it really did was make the curtain one of three equally stupid options. Restaurants can now get rid of the curtain by building a 42-inch-high wall or railing to physically separate the "eating" and "drinking" parts of the restaurant. They can also remodel the whole damn restaurant to create a ten-foot buffer zone only for alcohol, with no dining or children allowed. So if you want to get rid of the drink-mixing area your restaurant already has, all you need to do is burn the place down and rebuild it from the ashes. Who says government doesn't work for the people?