The MacPherson Strut
A MacPherson strut is a popular design for two main reasons: it's cheap to manufacture, and it does not take up a lot of space. This is exceptionally important in any front wheel drive as more room is needed for the engine. A car's suspension system consists of a variety of components; the ones that you have likely heard of the most are the struts. This is because they are typically replaced more often than the other components. The strut is the portion of the suspension system that serves to dampen the bound and rebound natures of a car that is travelling over bumps and/or around corners. The spring and the strut work together. The spring holds the vehicle up and provides the stability needed to keep the vehicle level while driving on the road. If the strut is completely worn and unable to provide any dampening forces at all, the car would be very bouncy. You could continue to drive a car like this however the springs are left to deal with quite a bit more force and might eventually break because the spring alone is not meant to deal with the type of forces that something like a pot hole could provide at higher speeds.
The way a typical strut works is by having a rod that slides in and out of the body of the strut. This sliding action is dampened by the controlled friction that occurs as a piston within the strut is dampened by a certain type of oil. The strut is a sealed unit; however, after time due to age, corrosion and general wear and tear on the seals that are used in the construction of the strut, the strut will fail. When you keep driving with failed struts, other parts start to wear more quickly. The spring is the first, the spring is holding up the vehicle and without the strut to back it up it is more susceptible to breakage. It will sag and let the car sit lower which causes the tires to wear on the inside much more quickly. You also might find that the car is scraping its tires on the inner wheel wells as the vehicle travels over bumps. The car will not handle as well when turning and this will put more stress on the suspension bushings and the sway bar end links.