I don't think it helps much in actual recoil as mentioned above, but it can help in felt recoil by not getting popped as hard in the cheek. I think there's a real value to decreased muzzle jump in just about any clay target doubles game.
From what I know, there's a bunch more surface area on most shotgun porting than rifle porting. So, I believe there is compensation for the decreased velocity of the redirected gasses by bleeding off more.
Lately, I'd rather bird hunt and can't stand porting in general, but when I shot a lot of doubles trap, it made a huge difference.
