[Yoda]

"Homer Kelley felt very strongly that all golfers -- not just 'good golfers' -- would benefit from Clubs with a stiff shaft flex."

What explaination did he give for that Lynn?

The stiffer Shaft better resists the Impact Collision and also promotes less Clubface deviation both prior to and during Impact.

Remember, for Swingers, Centrifugal Force is driving the Sweetspot, not the Clubshaft. It is functioning merely as a piece of string that, in fact, is being stiffened by the outward pull of Centrifugal Force itself. So, other than being of sturdy construction and for the reasons cited, Shaft Flex means little to the Swinger.

For the Hitter, though, Shaft Flex is mission-critical. He demands a stiff Shaft against which to push the Clubhead Lag through Impact.