Different screens need different details
A shopping app’s product list needs names and prices for many products. A product page may need one product’s name, price, photos, and first three reviews. With GraphQL, each screen sends a query listing the details it wants. The API returns them in one response: names and prices for the list, with photos and reviews added for the product page.
This can save the app from downloading details it will not show or asking separately for reviews. The API’s schema defines what can be requested, including connections such as which reviews belong to a product.
The server still does the work
GraphQL can also change data through mutations, such as adding a review. The server must gather the requested information, check who may see or change it, and limit queries that demand too much work. GraphQL gives apps flexibility, but its speed depends on how the API is built.