its the communications network that many of the devices and sensors use to communicate to the ECU and each other.
if you cut it, it MAY sever some essential communications. what if the ECU needs to see your speed when you hit the brakes and ABS kicks in? what happens if your engine stalls every time you pull up because the ECU didnt know you were moving.
there are hundreds of potential problems. and many people will ignore scott's warning, and this one. but its your car, cut away!