The steering and suspension systems of a car are not only important for safety reasons but also enhances the comfort level of the vehicle. The two systems are directly related to each other, which is why they are always referred to together.
Rack and pinion steering is almost always used with a MacPherson suspension system. The bottom of the steering knuckle still pivots on a lower ball joint, but the top of the knuckle is connected to the MacPherson strut. In this system the outer tie rod end is connected to an arm on the strut housing itself.
The MacPherson strut assembly replaces the upper control arm, front shock absorber and ball joint, increasing handling and responsiveness. It controls ride much the same way as a standard hydraulic shock absorber. It also keeps the front end aligned and eliminates, in some cases, the need for caster and camber adjustments. In most cases it also contains the front coil springs so care must be taken when you are replacing them.
The down side is that they will eventually start to leak and will require replacement. They generally last longer than a conventional shock absorber and that may offset the greater cost of the MacPherson strut assembly. As far as replacement goes, some struts have an internal shock assembly that can be replaced separate from the rest of the housing and others have to be replaced as a unit.
One of the main functions of your vehicle's suspension is to relay to the occupants a smooth, comfortable ride even when you're on a bumpiest of roads. More importantly your vehicle suspension's main role is to give the maximum opportunity for all four tires to remain in contact with the road, so that when needed, your braking, steering and driving systems are safe, effective and responsive when you need them most.