Yeah, it does. There is a probability of defects anywhere on the wafer. If 100% of the circuitry on a die is essential, then you have to throw away the dice where the defects occur. If you have redundant circuitry, then you can keep the dice with the defect by disabling the affected circuits.
If you look at the floorplan for the M1, the GPU region takes up a significant portion of the die. If a defect occurs just about anywhere in that region, it really only affects one GPU core. By disabling that one core, the die is still viable.
There are different ways of thinking about the economics, but one way would be to essentially think of Apple getting the 7 core dice for free. If they held to the 8 core spec, those would be lost yield. They still need to be packaged and tested, so the final SoC isn’t free, obviously.
