A degree signals you have a history of satisfactory performance of arbitrary tasks over a prolonged period. It can be a way to get less bad employees, though not necessarily better ones.
From knowing a little about recruiting, if you have a bachelor's degree and apply, they're willing to drop one of their employees who barely finished high school.
It's not worth it to replace an underperformer with someone else who'll likely underperform. But if you can start with someone you deem "better" because they have a slightly more expensive piece of paper, it's more worth the risk.
I thought conventional wisdom was always that service industry jobs don't really want people with degrees because they're more likely to find something better and jump ship quickly. "Overqualified."