Hiring a JNI developer is beneficial when you need to integrate native code (C, C++) with Java code. They can create high-performance applications, leverage legacy code, or access low-level system APIs. Their knowledge ensures seamless interoperability between Java and native applications, enhancing your software's functionality and performance. They can also handle complex tasks like memory management, debugging, and error handling in JNI environment. Their skills can be crucial for developing robust and efficient software systems.