Ever notice how a bunch of stupid drivers playing with their phones tend to lock to the same speed and wind up abreast of one another? Ever notice how you feel compelled to start rolling forward at a light even when it is still red simply because the car next to you started moving? When in fog, you are paying attention to lane markers if you can see them, but you are also paying attention to what the tail lights ahead of you are doing.
All of that is "station keeping".
And it's normally extremely important to give it priority--generally even over external signals and markings (a green light is only relevant if the car in front of you moves). It's the kind of thing that prevents you from running into a barrier because everybody else is avoiding the barrier, too.
Of course, it's also what leads to 20 car pile ups, so it's not always good...