I have seen some people claim that soy lecithin is waste product of soy.  They are wrong.  Soy lecithin is not a waste product, it is an extract of soy.  And it has many beneficial properties in the body.  For example it is lecithin that allows the cells to be flexible.  If we took all of the lecithin out of our bodies we would be rock hard. It is also a major component of myelin, which insulates the nerves, brain tissue, and bile; which is the component that makes bile an emulsifier.  By the same token lecithin lowers cholesterol, prevents gallstones, and increases the absorption of dietary fats and fat soluble vitamins.  Lecithin is also a rich source of choline, which is essential for the formation of the neurotransmitter acetylcholine.

In short a few of the benefits of lecithin include cleaning out the arteries, lowering cholesterol, preventing and dissolving gallstones, increasing memory, improving dietary fat and fat soluble vitamin absorption, decreasing body fat/weight loss, rebuilding the liver and preventing fat deposits in the liver, regeneration of myelin (important for MS and diabetic neuropathy), promotes breast health and improves prostate secretions, maintains cell membrane flexibility and controls movement of nutrients across the membranes, and phosphatidyl serine is lecithin is an important building block for the brain.  This is just a partial list of benefits.

Lecithin is found in other sources, but very few sources have high levels.  Eggs for example are a good source, but egg lecithin is extremely expensive.  Dandelion flowers are extremely high in lecithin, much higher than soy, but from a manufacturing standpoint is not a good source.

Lecithin is the active component of nonstick cooking sprays, and is used in numerous foods including chocolate.

There is not much difference between soy lecithin granules.  The primary difference is whether or not it is from a genetically modified source.  Some people are very afraid of GMO products, but not all are bad.

I generally recommend the generic lecithin granules to people, which runs around $6.00 a pound. The liquid and soft gels are highly diluted and should be avoided.