There ws a craze a few years ago on putting GE's onto domestic stereos, and even in-car systems. They work by adjusting an individual frequency from lowest to highest, so in theory you can tune your system to provide the sounds as you like them.
Honestly? Waste of time. Unless you have really sensitive ears - I'm talking sound-engineer ears here, you won;t be able to detect the nuances enough to make any real difference. They are used for live concert sound mixing where the ambiance of a room does make significant difference so the sound, and a professional engineer uses a highly sophisticated GE to mix the sound correctly.
For you at home, or in the car, trust the engineer who mixed your sound source to have done his job, and use the Treble and Bass to adjust the top and bottom ends to taste. If you haven't got a GE fitted, don't bother, and if you have, set all the bars to the middle and ignore it.