When to use a polarizer. Whether you are trying to get crisp clouds on a blue sky, reduce hazy, or eliminate glare on water a polarizer can do things quickly, when Photoshop can't.
It's a beautiful sunny day with light blue skies and white fluffy clouds, how to you get the sky darker without changing the exposure. Or maybe it is a hazy day and you are looking over a vast canyon, how to you cut down the hazy. How about a glassy lake with reflections on it, but you want to take a picture of the colorful rocks on the bottom. How do you do all these photos?
Our family went to the Grand Canyon for vaction, and I was VERY glad I brought my polarizer. (A Polarizer is a filter that screws onto your SLR lens.) It significantly reduced the haze over the canyon (see photos below). But it was also great for bringing out the reds of the canyon walls and the blue in the sky. The photo on the right is with a circular polarizer. If you prefer the light blue sky (like my husband does) you can take two photos, like the ones below and layer them in Photoshop, removing the sky from the polarized one.
It also it a great job of eliminated the reflections on the Colarado River as seen here.
It is the one filter I still own, post-Photoshop. Just isn't a way to remove the glare off the water and look through to the bottom on the computer, yet. Where would the details for the information come from? Any way, I highly recommend using a polarizer for such occasions.