Product sales when out of stock
When a product is out of stock, it cannot be added to an invoice. This makes sense at first, but there can be situations with incorrect stock status (data entry, returns not processed), and there is more on the shelf than the stock level says. Or a back bar item is "converted" into a sellable item on the fly.
An override would be good to sell the product anyway.
The stock level can be changed before the sale, of course. But this adds time, and not staff member may have permissions.
Thinking it further, some kind of special order would be possible with that: Client pays for an item ahead of time, then it will be ordered individually (we have a lot of special order hair items that will never be in stock).