I would like to better understand the reasoning behind what the author says here: A balanced 16-cavity mold costs 3-4x more than a single-cavity mold but only produces 16x the parts, which is why they only make economic sense above 500,000 units.
In this context, a cavity produces one part. A cavity can only produce, lets say, 200k parts. If you produce 400k parts, you only need a single mold, but you've only used 25k wear on each cavity, but you paid more for the mold instead of only 2 of the cheaper single-cavity molds.