Apollo Workbench is a tool designed to help companies develop their graph using Apollo Federation, reducing the feedback loop time when planning schema changes. It provides features such as composition errors checking, query explain, and mocking designs, allowing developers to work with subgraph schemas directly and understand the overall composition of the design without starting up services or writing code. With Apollo Workbench, teams can create designs from their graphs in Apollo Studio, add operations to designs, view query plans, and mock designs locally for development. The tool is designed to be used with a centralized schema registry, such as Apollo Studio's Rover, and provides insights into graph composition, errors, and query execution plans, enabling developers to work only with subgraph schemas and improve the development experience.