Hiring a FXML developer is crucial for creating intuitive and user-friendly GUIs in JavaFX applications. They are skilled in defining user interfaces in XML, separating UI design from application logic, leading to clean, maintainable code. With their knowledge in FXML, developers can rapidly prototype and redesign without rewriting significant portions of code. They also work well with design tools, enhancing collaboration between developers and designers. Their expertise ensures a smooth, efficient development process, resulting in visually appealing and functionally robust applications, ultimately improving user experience and satisfaction.