How does staffing connect to restaurant profitability?

Labour is one half of prime cost — food and labour together — and prime cost is the number that decides whether the model works. So staffing is not just a setup cost; the ongoing labour line, scheduled to covers rather than to comfort, is one of the two largest controllable costs in the business. Get the per-head cost and the schedule right, and you are managing the lever that matters most.

From Restaurant Staffing Costs: Visas, WPS and the Real Price Per Head — the full reading, with the method behind this answer.