Or, “more about those sunny days of summer”.
Why do you need a Polarizer (“Polarizing filter”, “Circular Polarizer”, “C-Pol”)?
Most lens filters bought nowadays (“UV”, “Daylight”, “Protection”) do nothing but protect against sand, snow, and rain. And sticky fingers. But one filter, the Polarizer, does something.
Put it on your lens and you see the normal scene (but you need more ISO, lower “F-number”, or slower shutter to compensate for the loss of light):
Now turn the polarizer, and suddenly, the reflections on the non-metallic part of the car, the windows, disappear!
Bit more importantly, look at the sky. Here’s the scene outside my home yesterday at 2pm:
And now I turn the front of the filter until this happens: look at the sky, and observe the green colour of the tree:
And that is why, especially on those blue-skies-with-some-cloud days, you should carry a polarizer!
(Can we do this is Lightroom? Yes – but then you get funny edges around the shapes. There’s no real substitute for a Polarizer in this case.)