* Checking whether each item scanned has satisfied a logical contract for a discount, some of which may be per-region, per-store, or even per-customer.

* If multiple exclusive coupons or deals are available, resolve the contradiction, preferably in favor of the customer.

* Check if any items or quantities of items require an ID to be shown before proceeding, and record information about the employee authorizing it.

* Update customer "rewards" data and generate any special offers so that you can put it onto their receipt.

And that's not even starting to get into all the other less-customer-synchronous stuff that you still need CPU power somewhere to do. Managing stock levels, orders, deliveries, price changes, anti-"shrinkage", employee shifts, market-research, status and repairs of freezer-units, operational logging and telemetry, every form of reporting/dashboard "strategic insight" stuff beloved by upper management...