Driving on bad ball joints can create a number of problems. Worn ball joints can cause other parts to become worn, increasing the cost of repair as well as potentially causing a driver to lose control of a vehicle.
Loss of Control
A bad ball joint will allow a car's wheel to move somewhat independently of the suspension. This can lead to a driver losing control of the vehicle as the tire not properly gripping the road. The risk is greater on an uneven surface; on which a wheel with a bad ball joint could "bounce" away from the roadway.
Tires will often show excessive and uneven wear on wheels supported by a bad ball joint. This is due to the wheel moving somewhat independently of the suspension. The tires will often show signs of improper wear before the ball joint wears to the point of making an audible sound.
A bad ball joint places more strain on a number of related parts. Further, until the slack in the ball joint is taken up, the suspension cannot dampen the wheel's independent movements. This causes a jolt that can add wear to the many integrated parts and lead to their premature failure.