I'ts all about presentation when you're serving up a delicious espresso libation. This starts with a clean cup, a perfectly extracted shot of espresso, silky steamed microfoamed milk, and a perfect pouring of the milk into the espresso. This is no easy task to master, these examples were taken a YEAR after I started training as a barsita.
Some argue the necessity for latte art. Yes, it is but an aesthetic addition to a beverage, but it also shows that the barista has had some training; and that separation between white foam and the brown crema of the espresso shows the correct amount of microfoam made it into the cup.