What it's normally used for
Choline is used by the body in a number of ways, including aiding nerve signaling, transporting triglycerides from the liver, maintenance of cell membranes, and as a constituent of nervous system tissues in early brain development. Choline is a precursor of acetylcholine, a neurotransmitter needed for nerve and muscle function, and a component with lecithin, which is needed for normal liver metabolism. Without adequate dietary intake of choline, there's a higher-than-normal risk of chronic liver damage and then eventual liver failure. Choline is vital in forming the very low density lipoprotein (VLDL) in the liver, which helps transport fat from that organ to cells throughout the body. Although VLDL is considered the "bad" form of cholesterol because high levels show an abundance of circulating triglycerides, if VLDL levels go too low, fat begins to accumulate in the liver.
What it does for Lucid Dreaming
Choline promotes acetylcholine, which enhances the expression of REM sleep. It's found as a supplement, and is's also found in some common foods such like eggs, bananas, soybeans, onions, potatoes and plantains.
Choline is believed to make dreams longer, and also help you remember them. A lot of lucid dreamers have found that choline and Galantamine taken together are the ultimate supplements for promoting lucid dreaming.
My own results
I take Galantamine and Choline after six hours of sleep. It's hit or miss on having lucid dreams or vivid dreams. My results can range from getting a massively vivid lucid dream to not even getting more vivid dreams. (Nothing guarantees you lucid dreams 100% of the time!)