Filters are somewhat out of fashion these days; color-correction filters have mostly been replaced by Photoshop work, graduated ND with HDR, effects with Photoshop effects, and B&W filters with Channel Mixer.
Which leaves the polarizer. And most articles I’ve seen on the topic point out that the polarizer does things that can’t be duplicated with other methods, and you really should continue to use it.
Back on a June photo expedition, which I haven’t put other pictures from up yet, I got perhaps the best example I’ve seen of how big a difference a polarizer can make.
Recall, briefly, that a polarizer blocks light polarized a certain direction. The filter is set up so you can rotate it, so that you can pick which polarization direction to block.
The classic things you can block are specular reflections (diffuse reflections tend not to be polarized) and sky at certain angles to the sun.
These pictures, not very interesting in and of themselves, demonstrate what a big difference this can make.
First, of course, you’ll see the huge change in the appearance of the water. Lots of specular reflections going away there!
But after that, look at the trees on the far side of the river. The ones without the polarizer look much duller. I think that’s because there are a lot of very small specular reflections from the leaves over there, that we don’t notice as such, but that reduce color saturation by diluting the actual leaf color with reflected sunlight. You can see similar effects in the roofs of the buildings on this side of the river. Consider especially the big one right against the bottom edge, showing through between the leaves on the right; with the polarizer, it’s mostly black, whereas without it’s quite bright.
As is typical of the perversity of the universe, the water is probably more interesting with the specular reflections, but the trees and houses are probably better without. Well, luckily that photo doesn’t seem (to me) to be going anywhere anyway, so it doesn’t matter.