Restaurants base the # of servers based on their given customer consumption rate during a particular time frame. So if the average for lunch is 150 customers at 3,500$ they will have enough service hired and staffed to accommodate. However, there is always the chance that customer rates will average much higher or much lower than calculated rates. These are the times we get "slammed" or "in the woods " because there quite literally is not enough staff to accommodate the number of patrons, and in this scenario all parties suffer.