What is the purpose of the roof drip moldings on my 2003 Toyota Tundra? Do I really need to install them?

I can answer my own question. You need the drip moldings on your vehicle. They are not cosmetic at all. As stated in my question, I just had my truck painted and the drip moldings on the roof were too brittle to put back on. I left them off and sure enough it happen to rain. I had water at both rear corners and water at the front corners. Actually, it was just wet or very damp. I put a wash rag at both rear inside corners of the cab. It was still getting too damp. I am trying clear packing tape on the front and rear area on the roof. Just a small enough piece to cover where the window seals and roof meet. So far, so good.