More control over your firearm. Better finger placement on the trigger. Improved trigger control. Improved prone shooting.
Look at all the top target shooting rifles. Then look at all the top military style weapons. You will find at least one thing in common...they all have pistol type grips or " thumb hole" stocks.
They just are not very " politically" correct for hunting. Of course I say this just as Benelli has taken the stock from the M-1 Tactical, applied some camo, added it to their line of hunting shotguns, and renamed it the " comfort/control" stock.
Go figure!