It's aesthetics mostly, I feel. But the tank does look great at night, if not a little too bright. I covered over the LEDs on my Coralife fixture to make them darker.
If you're looking for moonlights I recommend checking out this company. They sell online from there website and on ebay.
I bought mine from there ebay listing for my freshwater tanks and I love them!!! http://www.fishbowl-innovations.com/product/moonlights