Landscape photographers are romantics. They must be - they go a thousand kilometres to camp overnight in freezing bush so that they can get up at 3:30AM and hike through bush to a beachfront. Then they haul 500 Kg of equipments over wet rocks and stand there shivering while they are waiting for he sun to rise. They have $ 8200 sitting on a tripod in front of them on the slippery rocks and are waiting only an incautious moment to tip it into the sea.
Then they drive a thousand kilometres back home and spend week of nights in a dark room trying the HDR the result. This seems clear evidence of either romance or madness.
One of the symptoms of this madn... I mean one of the useful and perfectly normal items that every landscape photographer needs is the circular polariser filter. See the opening image for a typical polariser in operation.
The polariser makes blue skies bluer, green seas greener, and white bride's dresses whiter. Foliage loses the blue cast that Western Australian skies put into it and the colours seem much richer. They can also be used to see through water surfaces and glass shop windows to reveal the goods within. It makes everything look like it is straight from the pages of ARIZONA HIGHWAYS.
Good? Yes. Bad? Yes. WHAT?
Well, consider - if you want to see bluer skies and greener seas and fluffier clouds, all very well - you can produce this effect and good luck to you. It is charming but fraudulent. If you wish to represent what your eye actually sees in a scene, consider that your eye is seeing the light scatter anyway - remove it and you are interpreting rather than representing.
Morals aside, if you want to get the full effect of the polariser remember that it works most effectively at 90º from the sun. If you try to put one onto a lens that has too wide an angle of view it will work in one portion of the scene differently from another portion. You may be better in these cases to seek your colour enhancement by computer means further down the track.
Please note that the polariser filter and polarising sheets may be a real boon in art copy and scientific work - letting us see what the light scatter spoils. We are seeking science, not art. And generally don't have to stand on wet rocks to get it.