When I took my door panel off today, the paper that is installed between the panel and the door itself was in pretty rough shape. The putty sealer was also hardened and it fell off. I decided it wasn't worth re-installing.

What is the purpose of this paper, anyways? Is the idea to seal the interior of the door against moisture entering from the car interior [a la the vapour barrier in a house] or is it a noise lowering idea or is it to prevent moisture from reaching the back of the door panel. Whatever it is, I've never found this paper to be in any kind of shape whenever I've opened up a door and so it cannot be doing its job. And, by conclusion, it can't be all that important.