Hiring a HHVM developer can significantly boost your web application's performance. They can convert PHP into machine code, making your website faster and more efficient. These developers are skilled in managing memory errors and inconsistencies, improving your application's stability. They can also handle hot code detection and just-in-time (JIT) compilation, which optimizes frequently used code paths. Moreover, a HHVM developer can ensure seamless interoperability with Hack, a programming language developed by Facebook for HHVM. By hiring a HHVM developer, you can enhance user experience, increase your website's speed, and improve overall operational efficiency.