Online retailer Boxed, a competitor to Costco and Sam's Club, has attracted years of fawning publicity for implementing automation at its warehouses without laying off a single employee. It is even raising salaries.

But the company is shrinking the number of added workers required for expansion. That aligns with an axiom of automation — that jobs offering the best chance of rising pay are usually in industries that are growing and adding labor-saving technologies at the same time, before the number of jobs eventually declines.