I think it depends on the gun in the first place. Then there might be less necessity for fouling the barrel while hunting. As long as the ball hits the vitals everything is OK.
This is different for target shooters. Many swear by the necessity to have the gunbarrel in the same state of fouling "every" shot. That is why many first shoot a fouling shot, and then whipe the barrel in the same way between every shot. Certainly shooters who follow the Dutch Schoultz papers will strive to obtain the best possible consistency. That goes as far as precise preamesured powder loads, measured ball weight, consistency in shootin stance, breathing controled, etc etc... This consistancy also helps concentration and ease of mind ... some call it even a bit of a 'zen' thing ... I wouldn't go that far!