The force required to turn a car's steering wheel is greatly reduced by utilizing a power steering system. Internal steering components should be well-lubricated to guard against failure, which is why a hydraulic pump pressurizes the power steering fluid.
However, with the significant heat generated due to pressure build-up, the fluid begins to degrade. Particles from hoses, seals, and gaskets are deposited into the fluid, resulting in deterioration of the power steering system.
A power steering flush is recommended every 30,000 miles. The DIYer can replace power steering fluid; however, it's usually better to have this job done by a trained auto service technician.