The buying price changes daily; the menu does not. A system that carries this morning's auction price onto tonight's board stops a dish being sold below cost.
Shrinkage is the real margin. Live shellfish loses weight and sometimes everything, and without recording it by species a kitchen believes a dish is profitable when it is not.
Ordering by weight is a till discipline of its own. Scales at the counter, price per kilo and a receipt showing both end the argument over the bill.
Christmas pre-orders are a second business. Deposits, collection windows and a list nobody forgets decide the month of December.
Traceability is both a duty and a selling point. Origin, market day and batch get recorded anyway, so they may as well appear on the menu.
A table of twelve needs different tools from a table of two. Pre-ordered menus, deposits and kitchen lead time are management, not service.