I see acceptance sampling as "
insurance" - paying a little to mitigate major problems.
If the situation is "healthy" - the supplier's processes are in control and producing items to spec - then the shipments coming in will automatically be fit for use. Acceptance ampling is actually
counterproductive here! The money spent on testing will never find a bad lot (because there are none!) but it will occasionally reject good lots, adding costs for both consumer and producer. It is a waste of money. Just like health insurance is a waste of money
as long as you stay healthy!
If the situation is "ailing" - the processes aren't in control and the shipments have varying quality - then you will get good shipments and bad shipments. Now the "insurance" is vital. Receiving an "unhealthy" shipment will cost you money and time, but it will cost a lot less than paying the price down the road for the bad situation.
I suppose you could equate the deductable to the style of sampling you do. A high deductable is like a relatively weak sampling plan (like "reduced inspection" or "Level I" in Z1.4 language). With a high deductable (weak sampling plan), the premium (testing expense) is low, but each accident (bad shipment) results in higher out-of-pocket expenses.
Just like with insurance, the amount & type of insurance depends on your lifestyle and willingness to take risks. If your business is "young and carefree", you might live a little dangerously and skip the insurance. Similarly, if you are in a "trusting, monogamous relationship" with a supplier, then you may now need as much insurance. If you take up with a new, unknown salesman every month, you might just want a little more "health" insurance.
I suppose we couls say that SPC is like getting yearly (or in this case daily or hourly) physicals. If you check your "vital signs" on a regular basis, then your know how your health is doing and you can head off problems before they start.
OK, OK. I probably pushed the analogy a bit far, but I think it works pretty well. Preventive maintainence keeps you healthy, but a little insurance may still be a wise investment.
Tim F