I've been dubious of the worth of buffers myself, but...
I built a pistol that kept locking to the rear--the bolt seem to jump up out of the rails. I think I may have installed the trunnion a bit to the rear, or perhaps it was out of spec (as it is a custom trunnion designed specifically for a pistol).
Anyhow, tried a blackjack and it its been fine. My take is that I'll still not use one if it fires without it, but I've learned they do have their uses.
(I know, I know, if it was a properly funtioning firearm it wouldn't likely need it. And I suppose I could drill out the trunnion, weld up the holds, remeasure and redrill and rerivet the trunnion back in, and as fun as that sounds, the buffer has done the trick.)