Steering and Suspension
Possibly the most over-looked parts on any car. Suspension components can be expensive to replace and therefore easy to put on the back burner.
Ball joints and tie rod ends are very important parts that should never be overlooked. The ball joint is responsible for allowing the wheel to pivot as you turn and carries a lot of the vehicle's weight on it's shoulders. Early warning signs of a defect can include a squeak when turning. As the joint wears more, a clunk over bumps or when turning can develop and once there is enough play in the joint, a vehicle can begin to pull left or right while driving. If left long enough, it can separate causing a potential accident (See above photo).
Tie rod ends are equally important to maintaining control of your car. There are inner and out tie rod ends and they are the link between the steering gear and the tire. As you turn the steering wheel, the steering gear moves these parts either left or right allowing both tires to turn in unison. If there is play in any part of this system, the steering wheel may seem loose and not as responsive. Again, worst case scenario is if an outer tire rod joint were to separate, you would lose the ability to keep that tire pointing forward possibly ending in a vehicle accident (See below).
Shocks and struts are always the last thing to repair on a car due to their perceived main purpose being ride quality and unless completely destroyed, not essential. Defective suspension can lead to poor tire wear, reduced vehicle responsiveness in cornering and most importantly, longer braking distances. If the suspension is not properly forcing the tire to contact the road, the back of the vehicle can lift more under hard braking thus reducing the effectiveness of the rear brake system increasing total braking distance. Properly functioning shocks and struts help minimize this effect allowing the brakes to work as designed and minimize stopping distances.
We've all seen someone slam on the brakes... the front dips and the rear rises. The brakes can only work if the tires are adequately touching the road!