A GSON developer uses Google's open-source Java library, GSON, to convert Java Objects into their JSON representation and vice versa. They use this library to effectively convert complex nested JSON data into equivalent Java objects that can be manipulated in code. This process is known as serialization and deserialization. They also handle JSON parsing exceptions, manage null object fields, and control object field visibility during conversion. GSON developers streamline data exchange processes in web services, mobile apps, and other software that rely heavily on JSON data, thereby improving data consistency, efficiency, and reliability.