Driving a vehicle with a cracked windshield can be dangerous. Cracks can cause windshields to shatter with even light impact, and in some cases the vehicle's roof can cave in.
A crack in the windshield weakens the structural integrity of the windshield. If there is a wreck or even a small fender-bender, the airbag can deploy, hit the windshield and send shards of broken glass flying all over the passengers in the vehicle. In some newer models of vehicles, the windshield is factored in as part of the vehicle's support structure, so if a windshield weakened by a crack gives out, the entire roof of the vehicle can cave in on the people in the vehicle.