Being a veteran of both Iraq Wars, I have learned that eye protection is paramount. A good quality set of eye glasses can serve multiple purposes on traffic stops and any other outdoors call.
They will protect your eyes in case you are attacked, or if you have to fire into the vehicle. Having conducted and performed live fire exercises involving vehicles, flying glass and debris is a real hazard.
Polarized glasses help cut through the glare from windshields and actually help you see into tinted vehicles better in strong sunlight. Polarized glassses can also assist in finding certain kinds of linear oriented evidence (such as skid marks on roadways).
Polarized glasses don’t have to be dark in order to protect you from temporary blindness caused by the sun. Lighter shades of polarized sunglasses can even be worn on cloudy days to protect from UV rays (which are still present).
The bottom line is...sunglasses will not make you miss a gross movement of a suspect such as pointing a weapon, but could save your eyesight, which can never be replaced.