One of the top reasons you should be wearing sunglasses is to protect your eyes from UV damage. Long term exposure to UV rays is linked to eye health issues such as cancer of the eye lids, cataracts and macular degeneration.
Polarized sunglasses block glare reflected from flat surfaces like roads or water. This is what makes them different from standard (non-polarized) sunglasses which will protect your eyes from bright light but will not reduce glare.
With the low angle of the sun in the sky or reflected off the road surface, even using a driver’s car visor is often useless. The best remedy is to have a pair of polarized sunglasses ready to hand in the car.