I like the way LEDs make the colors pop. When I first put them over the tank I thought they looked almost artificial, all those glowing polyps! It didn't take long to get used to it. I've had a few issues with the startup of this tank, so I'm not so sure about long term health. The past 3 or 4 months has been great.
Then there's controllability, less heat, no bulb replacement cost, lower electrical cost (maybe), the shear joy of lighting my tank with something I made myself
Not seeing the downside yet... maybe later?