disadvantages would include:
limits development - ie you can't build houses, stores, factories, etc because it removes wildlife habitat. can't drill for oil or mine or farm on land that wildlife use, so it limits natural resource gathering. can't build dams for flood control or recreation or anything if the land is needed for wildlife. can't build roads through some places, so it means people can't get where they need to go by the best route.
advantages would include:
maintenance of ecosystem, diversity of species, natural beauty