I removed mine several years ago and eventually sold it because I decided to not put it back on...ever. I did find some rather fine, 1/8 inch I think, stainless screen on Ebay to cover the hole where the timing belt is. Just in case a stone happened to rattle up somehow into that tender spot. Aero? I doubt it. Maybe, but it makes access MUCH easier. As well as if something starts leaking being able to spot the source. On my car anyway, '88, the undertray does restrict access from someone if they knew what they were doing, to the fuel pump and lines and electric connections for it. But I never leave my car for any length of time, and never park in questionable areas. The undertray is surprisingly heavy for what it is. As far as cooling, I think that's why the holes are cut where they are, for more air to exhaust manifold. I've not noticed any consequences and I've had it off for quite a while. There may be an argument about this, but, bottom line, It's my car, I think I'll do what I want with it. I recommend you do the same.