Quite the difference
I took this shot to show a friend the impact the polariser can have on some images.
Now I know this is a pretty extreme example, but a good example of the difference a polariser can make. It was shot in Aperture priority, so the metering made an adjustment due to the reduced amount of light with the filter attached. I have used a circular polariser and taken one shot with full polarisation, then rotated the filter 180 deg to no polarisation. In Lightroom I have applied the same adjustments to both images, then layered them together in photoshop.
I have taken the shot in the right scenario that maximizes the effect of the polariser. The sun is perpendicular to the view of the camera. This isn’t hard in Queensland as the sun gets straight up high pretty quickly, so nearing midday looking in any horizontal distance will produce strong polarisation.
Yes, it also darken the skies and that can be one other benefit but it can reduce smog and haze, really depends on the shot and atmospheric conditions.
Foliage in landscapes really benefits from reduced glare, giving a more even saturation of colour.
Whether or not you should use a polariser is your decision. Personally I know there are times when it can really enhance the type of shots I’m taking, especially during sunny day outdoors… Other times there is no benefit and it can reduce the amount of light making it to the camera, which can cause it’s own problems. The one thing is for sure, the effect of a polariser are pretty much impossible to duplicate in post.
If you are shooting rainbows, the polariser will eliminate the rainbow completely, but at 180 deg from that the rainbow is actually intensified.