Lecithin, evening primrose oil and some other EFA sources can alter hormone levels in a very small percent of the population. This can definitely affect mood.
For the people who have no problems with lecithin though, which is the majority of people, lecithin is great stuff. It helps with building up the brain, myelin, acetylcholine, and it helps the liver and provides flexibility to cells as well as regulating transport across cell membranes. Lecithin is also the component of bile that makes bile a fat emulsifier, it lowers cholesterol and helps to remove arterial plaque.