The OEM bushings will become soft overtime allowing movement in the steering rack. This could potentially take away valuable feedback from the driver, causing excess play in the steering wheel. The Whiteline bushings will tighten things up, and you will see improvements in turn-in, but it makes for a better driving experience.
Please keep in mind that with harder bushings, inherent vibrations can be transferred into the vehicle.  Included in the kit is a tool to assist you with a simple installation.