A BSON developer is crucial for managing data in applications that use MongoDB, as BSON is the binary representation of JSON-like documents. They ensure efficient, organized data storage and retrieval by utilizing BSON's types and binary data storage. This leads to enhanced performance in large-scale applications. BSON developers also enable faster data transmission over networks and easier traversing through hierarchically structured data. Their skills are essential in creating robust, scalable applications, improving data handling and overall system performance.