Hiring a Knockout.js developer is beneficial due to the framework's ability to create rich, responsive display and editor user interfaces with a clean, underlying data model. The developer can provide dynamic JavaScript UIs with the Model-View-ViewModel (MVVM) pattern, making the code more manageable and easier to evolve over time. They can create complex dynamic web applications with great ease and efficiency. Moreover, Knockout.js provides automatic UI refresh, dependency tracking and templating features, which can significantly enhance your web application’s user experience. Hence, a Knockout.js developer can be a valuable addition to your team.