i often see wire cable on 4WD, Landies mainly, running from the corners of the windscreen to the bullbar. Is this a "stop tree branches poking me in the eye" thing or what?
They dangerous in an accident. Off-road they are more likely to catch tree branches between them and the car than going over the top. The windscreen already acts as a natural ramp for limbs to go over the top. Unless you are doing it for looks, I would leave them alone.