Doesn't really apply in this case.

TSMC charges per wafer. If yield improves, that means each wafer will have higher quality chips, on average. Which could mean less junk chips and/or more chips that will make it to a higher bin (which could mean more speed or less that needs to be fused off due to a flaw).

Also, you're not the customer they are talking about. They mean their customers, like Apple, AMD, Nvidia, etc.

Though you might see some savings because higher yields means inventory levels increase, which could mean a lower optimal price on the supply/demand curve. Even if the MSRP is lower than the optimal price, it would still mean less opportunity to scalp the chips for profit.