MooreTrucker said:
Which means less-than-optimal grapes?
Yes, insufficient phenolic development. Sugar may be there, but not enough of the "good stuff" that makes for good wine. It's not a completely straight forward metric, but in general, lower yields tend towards higher phenolic ripeness. I think Napa shoots for 2.5-4 range most years. In 2015 they were 40%-70% off those yields. Bordeaux AOC is 3.7 or under (I think, going by memory) In contrast, much of West Texas is 8+.
"Optimal" is a price/production matrix. In 2015 when Napa had to go really low yield because of extended drought and heat (resulting in really early harvest) they complained that it's not an economically viable model to go under a ton per acre. Which is true given $500,000+/acre vineyards. Texas, on the otherhand, can go low (Equitas Vineyard west of Fredericksburg is architected to 1.5 or fewer.