A GraphQL list returns many objects, and a resolver for a related field may query once for each object. One list query plus N related queries gives N+1 calls. The screen may look correct while latency grows with list size.
The demo compares separate related lookups for three rows with a request-scoped batch. A batch loader collects keys, queries together, and maps results back to each key.
When to use
Check for it when database calls grow with the number of rows in a nested GraphQL list.