Explain why nomadic tribes need to move from one place to another

Explain why nomadic tribes need to move from one place to another. What are the advantages to the environment of this continuous movement?

Nomads are people who do not live in one place but move from one area to another to earn their living. Their main occupation is cattle rearing for which they need availability of water and pastures for grazing their animals. When the pastures get depleted, they move to another place with their animals, looking for pasture and water. When the water and pastures get depleted, they move again and keep repeating the cycle.
Advantages:
(i) The movement of the nomads allows the pasture to regrow and recover.
(ii) It helps to protect the ecology of the environment.
(iii) It prevents the overuse of pastures.
(iv) The cattle by their dung help in providing manure.