Polarizer reduces glare from the object surface.
It will also increase contrast of the sky and make water surface clearer.
This is how you get a deep blue sky picture
Here are some comparison pics.
They are uneditted.
BTW, you will need a "circular polarizer", NOT "linear polarizer".
w/o polarizer

w/ polarizer, notice the windshield and hood

w/o polarizer

w/ polarizer.

w/o polarizer

w/ polarizer, notice the clouds, sky color, and water surface