That's CS Lewis isn't it?
As I recall he said "I don't pray for what it does for God, but what it does for me "
However the OP was about the effect upon others, which various studies have shown to vary from essentially zero, to noticeably negative.
That result is consistent with the Abrahamic view as rather elegantly explained by Douglas Adams as in:
"I refuse to prove that I exist," says God, "for proof denies faith, and without faith I am nothing."
Actually, it wasn't that which led me to the view that the Christian God cannot have free will, let alone be nagged into submission.
It was a SciFi story by Larry Niven (Protector, a classic). He postulates an extreme upgrade to humans where they become very much smarter. Such people find themselves with fewer choices, since most of our "choices" are based upon ignorance of what their consequences might be. Enough that if we understood more of what we did, we simply wouldn't do most of them.
His logic is impeccable, but his information theory and biology suck big time.