According to the Specialty Coffee Association of America, "coffee professionals are all employees who work at their shop under direct supervision" and are qualified because they have undergone an apprenticeship program that includes working with espresso machines.
A coffee barista will use their expertise in coffee to prepare espresso drinks. They understand the importance of using the correct grind for each individual brew type. They know how to properly manage water temperature so that it is not too hot or cold when it is exposed to ground beans during brewing. Lastly, they are experienced in pouring milk into a variety of different drinks-from lattes to iced coffees.
So this person would know how to make espresso drinks correctly, clean equipment properly, maintain inventory levels appropriately, order supplies for back stock so they never run out, reconcile all cash drawer transactions daily - essentially having complete control over the process from start to finish. And if you don't think it's important enough for people to be trained in these skills - just look at any Starbucks store late during the morning or afternoon on a Friday or Saturday! A lot can happen in three hours and all handle by baristas.