Hiring a MarionetteJS developer can greatly enhance your web application development. They specialize in simplifying the Backbone.js framework, making it more efficient and less time-consuming. They can construct complex user interfaces, manage application state, and integrate RESTful APIs. Their knowledge in handling MarionetteJS’s event-driven architecture can help in building scalable and maintainable applications. They are adept in reducing boilerplate code, thus making your application lightweight and faster. Their expertise can significantly contribute to bringing your vision to life, providing a seamless user experience.