This pic may help you see how the use of light is what affects the look of the image, when using Live Composite mode.
This total exposure was about 3 or 4 minutes long (made up of many 4 sec exposures as a result of Live Composite). The lit areas are bright and would never look overexposed, even if I kept going for an hour or more at the same iso and aperture and shutter speed settings.
Camera is in the same position as the one posted above - with the same settings. Nothing changed except, that I took this pic after the one above —- when it was totally dark and the ship had been moved into position and the tugboat had docked on the right side. There were no moving or brighter light sources during the exposure (just a little bit of streaking on the boat lights from its movement), to make it look much different than a time exposure - except there was no need to worry about how long the shutter was open before overexposing.