Sky gives the whole scene that open expansive look which less definition fails to portray. I especially like it because it is how my sky looks with a red and I now know that someone else gets what I'd regard as a natural sky look. I always find it worrying when books talk about red giving a "near black" look and otherwise implying that a red gets you an extreme almost unnatural look to sky.
No-one seems to say this about colour shots, even those without a polariser, which give a vivid blue sky and white clouds. " Just as I remember the day" is the usual comment instead. Frankly yellow hardly ever does it for me.