The strut on an automobile is basically a shock absorber assembly for your car. However, the shock absorber portion, itself, is just one part of the strut. The main function of the strut is to dampen the bouncing of the vehicle when it travels over uneven surfaces.
The strut assembly combines the coil spring, the upper and lower coil seats, the strut bearing, the strut mount and the strut boot.
As in any case with mechanical devices, after wear and tear and aging, the strut and its components will weaken. This causes side effects shown as increased tire wear, poor rebound effects or "body roll" and lack of steering stability.
It is important to have the struts checked regularily to maintain your car's performance and safety.