You need repeating pattern due to how steppers work. Theoretically you can have different chips, but they will be distributed evenly. And "yield" in this case

You need repeating pattern due to how steppers work. Theoretically you can have different chips, but they will be distributed evenly. And "yield" in this case is not how many chips can be placed on a wafer, but how many of them will not have defects in critical areas.