If you want a view that consists of multiple entities. Example: a view that displays a customer with his last 5 orders and current inventory count for the items in those orders. That's probably 3 entities (customer, orders, inventory). Sure, you can do this with REST but typically it will require calls to 3 different endpoints to gather that data. A graphQL server can serve the same data with 1 endpoint using a custom graphQL query. I'm not saying one is better than the other; just trying to give you an example.