Wiper blades should be changed every twelve to twenty-four months, depending on weather conditions and the quality and material of the blades. Over time, wiper blades lose their ability to clearly remove rain, snow and other debris from your windshield. Environmental factors, like UV and ozone cause wiper blades to age.
When a blade is past its physical prime, it will begin to crack or come apart. If unchanged, a cracked wiper blade will eventually come off completely allowing the metal wiper arm to permanently scratch the window. Being able to see the road ahead clearly is the most important safety aspect of driving. Faulty wiper blades could leave you blind in a sudden downpour or at any time bugs and other debris may obscure your vision. From an environmental point of view there is no impact of driving with old wiper blades.