A Force.com Migration Tool developer uses the Java/Ant-based command-line utility to move metadata between a local directory and a Salesforce organization. They are responsible for migrating changes from a sandbox to production environment, managing version control systems, and creating repeatable processes for deploying changes. They also handle the retrieval and deployment of metadata, creating and managing scripts to automate these processes. The developer may also need to resolve any issues or errors that arise during migration. The end goal is to ensure smooth, accurate, and efficient migration of data and changes within the Salesforce platform.