Nick a dark lens will just cut down ambient light passing through it, but if it doesn't have a UV filter included that will pass through the lens unhindered by the tint.
Without getting too technical (I.E. what I can remember!) When light is reflected off a surface say water, snow or a bonnet for example, the lightwaves are scattered causing the visually disturbing glare we are familiar with. Polarising lenses have their filter rotated into position to eliminate the horizontal reflected light only allowing the vertical light through to reach the eye. This will eliminate the glare giving a clearer vision, better contrast and colour definition and overall improved visual comfort.
So they are fantastic for snow and water sports and great in the Mog. However, there are some some drawbacks. They will show the stress marking on toughened windscreens and block some display screens. My Maui Jim's, both prescription and non-prescription, block my radio screen but not my phone, so no real problem.
Personally, I prefer polarising lenses for greater eye comfort when driving in the sun.
