Lecithin will indeed increase choline levels in the brain, which leads to improved memory and attention.
This effect is particularly visible if you smoke pot. No more memory holes, or almost
Choline levels are usually OK with most people, but any stress (mental, physical, gym, no sleep, drugs etc) will lower them.
As with most things (vitamins, Omega 3...), beeing "OK" doesn't mean you have an optimal level of these, far from it. Choline is brain food, and while few people really starve their brain from it, few people actually give their brain what it really needs to be efficient.
Also, as you age, you get less efficient with choline production and usage, and the difference will get even more obvious from there.
Lecithin also increases the production of sperm in males
It is a good, basic supplement to take all life long.
It is the basis of most nootropic stacks. Without a sufficient dose of Choline, Piracetam, Aniracetam etc will only give you a headache, or you just won't feel anything from them.
Lecithin is a good source of choline, centrophenoxine is better, alpha-gpc is the best (this one is a soft nootropic by itself, really good stuff).
Have fun.