A MobX developer uses the MobX library in JavaScript applications to manage states efficiently. They create observable states and define reactions to changes in these states, enabling automatic UI updates. They encapsulate business logic in actions, ensuring consistency and undo/redo functionality. Developers use computed values to derive data from the state, optimizing performance. They handle asynchronous actions and side-effects within the framework, facilitating complex application behavior. Their work simplifies state management, making applications more predictable, easier to understand, and debug. They work in collaborative teams, often using React for UI development, to build robust, scalable, and maintainable applications.