Well, they stop the front wheels toeing out under braking, give better steering feel and also, because they are adjustable, you can dial in more castor which will give slightly heavier steering and make the steering centre quicker.
That good enough? If your old ones are shot they leak silicon out and its also an MOT failiure. Heres a pic
I have a set on mine that Gary at APT made for me. I didnt know that they fitted the S14 at the time
You dont have bushes, they do away with the std bush and replace it with a spherical bearing (aka pillowball). They also have turnbuckles so that you dont have to remove them from the car to adjust them (mind dont have these)
They replace the stock tension rods on the front suspension, you know, the big rod thing that sticks forwards of the bottom arm with the big rubber bush on the end.