What it's normally used for
Because Chocolate has a lot of fiber, dark chocolate can actually help keep you full, making you eat less.
Dark Chocolate does this even better than milk, and it might even lower your cravings for sweet, salty and fatty foods.
Dark Chocolate is even good for the skin. The antioxidants, flavonoids found in dark chocolate provide protection from UV damage from the sun. (Yes, you do still need the sunscreen!)
Now you can eat chocolate withy out feeling guilty!
What it does for Lucid Dreaming
Some lucid dreamers report that it helps generate lucid dreams. How it does it would be any ones guess.
One idea is that it gives you a higher level of dopamine which then improves the chances of lucidity.
More dopamine gives you more comfy feely, sexual dreams, and they can be more vivid; which then gives you a chance to have a lucid dream.
Chocolate also increase serotonin levels, which when taken before bed, give you the REM-Rebound effect, giving you more vivid dreams.
Dopamine+serotonin = lucid dream heaven!
My own results
I've tried this twice. Once I took Chocolate after six hours of sleep and had two short lucid dreams, and as the chocolate started going in to effect, they got more vivid and easier to remember. I call this method CHILD, CHocolate Induced Lucid Dream!!! Got kids? Easter is a great time to try to get them into Lucid Dreaming starting with this method!! On the night I took the other half, I took it before bed, remembered just one dream, and it was not more vivid.