It depends what you're trying to do. If you're trying to engage a single target as accurately as possible with little or no time pressure, then the forward grip isn't for you. In that case, you want the traditional Standing Position, with the strong elbow up as high as your ear, the support elbow braced on your hip, and either a palm rest or the gun balanced on your fingertips.
The trouble with that, however, is that although it's steady, it's also slow. Slow to build, slow to recover from recoil, and nearly impossible to shift targets. What the forward grip gives is control over the gun, when you're swinging quickly between targets and making multiple rapid shots.
It may be best to think of it as a carbine technique, for close fast work, rather than a rifle technique.
PS - In addition to 3 gun and tactical shooters, top Cowboy Action shooters use a variation on the forward grip. Specifically, they grab out at the end of the forearm, and pinch into the gap between barrel and mag tube with thumb and forefinger. That gives enough purchase to really crank the gun back into the shoulder, which helps to hold the sight picture in some sort of alignment while swinging the gun around like a maniac, and pumping the lever like a demented monkey. Oh, I suppose it also helps control the awesome recoil of the .38 Special.
Of course, what the forward grip giveth, the forward grip taketh away something else. For a three or four second run, it's great. Longer than that would be exhausting in short order. Also, all that muscular tension is the enemy of precision at any distance. Far better to shoot with a tight sling and a loose body, then.