1. Concentrated proteins with the exact amino acid balance needed by your body.
2. The ability to get all the nutrition you need with a small volume of food (very important for folks with medical conditions giving them small volume stomachs)
3. Dietary cholesterol, but it has been shown that if you are not overeating that the dietary cholesterol does NOT contribute to serum cholesterol. In fact your body breaks it down and synthesizes almost all the cholesterol your body needs on a daily basis. (We're you aware that you NEED cholesterol?)
4. It tastes great, if well prepared (but that can actually be just as true of plant based foods)

I could go on, but that's enough.

The other side of the coin:

1. Plant based diets are never too low in fiber.
2. Production of plant foods is less expensive and uses fewer resources of the Planet.
3. For most people eating plant based foods can be just as healthy as eating animal products. (But not for all, some folks can't eat enough volume to get adequate nutrition from only plant products.)
4. It is not a simple thing to keep ones nutrition balanced eating only plant products. It takes lots of self education, and care in what one eats. Ignoring this when eating only plant based foods often results in some form of nutritional deficiency. The average person follows a vegan diet only until.his doctor tells him he's deficient in certain nutrients and he better go back to animal products or else.