If you look at the size of the box, related shafts running through it and the pitman arm, you can see that these items in and of themselves are pretty stout. The chances of them flexing is slim. So that means the mount they sit on must be flexing around as the tire resists movement. If you mounting bracket is properly braced to resist deflection, the support bearing is moot. If your car is all together and finished and you want to firm things up, the bearing support is a convinenat answer. It your engine is out and the suspension all apart, proper bracing can achieve the same results for $10 worth of metal and an hour with a welder.