What is the purpose of the somewhat large plastic cover that is located under the engine? You have to remove it when you change the oil.

I changed the oil on my 97 E320 last weekend for the second time. One of the front screws has not fully engaged into the metal reciever. After the first oil change I guess I replaced the screw well enough. The second time...the cover came loose and it started to flap when I drove the car. I have removed the cover and wonder if its necessary to replace it.

And another thing. On the E320 the oil drain plug is partically concealed by another plastic cover that extends to under the front bumper. I have not removed this cover the last two times I changed the oil. When I drain the oil the oil causes a mess because it partially hits this cover as it drains. Does everyone take this piece off too when they drain the oil, or am I missing something?

Thanks