I've often thought about this when assembling Ikea furniture. I have never been shorted. There's got to be someone at Ikea with the job of calculating the target acceptable ratio of over/under supplying small hardware pieces. I figure they can probably give out thousands if not tens of thousands of extra little screws/dowels/plastic bits before it exceeds the cost of missing just one. Between the cost of a support call, maintaining a supply of spare parts, labor and shipping to send out replacements... not to mention the less tangible to calculate loss of reputation to the brand. Quite interesting to think about at scale.