Have you ever driven with the wheels toed out? Basically it makes the front end twitchy at speed. It will respond and turn quck, but its not a stable feeling. Makes you feel like your going to wreck. Thats what happens when your going through rough terrain on a banshee (or anything that has bump steer). Running 1/2" of toe in keeps it from being that bad, but the more toe in you run, the less responsive the steering feels.
If you've ever seen those pics of Sundahls banshee frames, he basically elminated all bump steer by crossing the a-arms over.