Disadvantages? There are NONE.
To the advantages listed by Flickr, I'd add these:
(1) less money spent on food; (2) making the moral decision not to condone or give money to the (factory farm) corporations that perpetuate horrendous animal cruelty and unsafe (for humans) animal husbandry practices for obscene monetary gain; (3) delicious meals that include plenty of protein through choice of appropriate vegan foods; (4) if enough people became vegans, it might shut down those damned factory farms I mentioned, which would not only stop the animal cruelty, but would immensely benefit humans and the environment (facts about the animal sewage lagoons alone would make an informative, but nauseating, hub), and enough vegan foods could be grown to feed the hungry around the world.
One more thing about all that animal protein: unless the animal is humanely raised in a natural environment (pasture-raised, grass-fed), and not fed animal byproducts or GMO corn, not shot up with antibiotics and hormones, all that protein carnivores are eating is extremely unhealthy and is causing their bodies irreparable harm. If more people actually gave that some thought and acted on it, cancer and heart disease deaths might decrease significantly. By the way, Flickr, thanks for the referral to the Fuhrman and Gerson theories. I'll check them out.