The part you are talking about is a piece of crap, but it does protect the low hanging transmission lines that go to the cooler infront of your radiator. If you plan on going offroad, these lines must be protected via skid plate or rerouted out of the way. The reason most guys don't know what you are talking about is because they ripped it off wheeling before the ever knew they had it.
I actually made a replacement one out of metal and reinforced it with some cheap angle iron and gauge metal welded to the frame. It looked good until I put the body lift on. No it hangs way down and I'm gonna have to we bend the mounting tabs and drill new holes. I'll take pictures later to give you guys a better idea what I'm talking about.