The Request You Made 100 Times
A backend-for-frontend layer is one of the easier architectural decisions to get right. Each client gets a service that speaks its language, the domain services stay clean, and every team owns a box with a clear border drawn around it. An architect reviews the diagram and approves it — and the diagram is correct.
This is a field story about what the diagram doesn't show. Four correctly-written service calls, each behaving exactly as designed, turned one screen render into roughly a thousand queries against a sharded collection. The screen stopped loading, one collection's query time dwarfed every other collection in the cluster, and the ticket said "MongoDB is slow."
MongoDB was not slow. Nobody had ever counted what one user action actually costs.