The difference between four minutes and two minutes is not important to me. However throughput is very important. Not to me, but to Starbucks. From Starbucks' perspective, their business is dependent on how many orders Suzanne can prepare in a given amount of time. Workers are the major cost item.
Customers are the major income item.
The more customers each worker can process, the more profit Starbucks makes. Starbucks likes profit. I can't blame them. A worker can prepare a customer order in 90 seconds. Longer than that, and they will leave the store.