forcing cone work is done to reduce recoil...you are flipping a coin to see what happens to your pattern. usually nothing drastic. but it does not in all circumstances improve the pattern and in some instances it goes the other direction.
Idk what the theory behind it is now but I started doing this in the 80s. Back than Mark Basner was the shotgun man. The cones were opened not for a reduction in recoil, it was to improve pattern. You did lose slight velocity though. Since than I’ve had and still have multiple guns that way. No way it could ever hurt having a gentler entry into a barrel as opposed to rattling its way to a start.
I’ve never seen things get worse. When Mark did em for me I’d send him barrels. They always improved.
Now as I said I don’t buy guns now without it so I can’t compare before and after like that. Many guns come elongated though when turkey specific or just wing shooting type guns also have em lengthened.
Ithaca, Browning, Mossberg, Fabarms to name a few off top of my head