CCJW is used only in the US. CCJW is used by the US Branch service department as their corporate portion. In other countries, it would be a different corporation, such as in Britain it is the International Bible Student's Association.
In the US there are 8 main corporations used by the US Branch Committee or Watchtower for different functions. They are Watchtower Bible and Tract Society of Pennsylvania, New York, New Jersey and Florida, Religious Order of Special Full Time Servants of Jehovah's Witnesses, Kingdom Support Services, CCJW. Then there is one for the cemetery at Walhkill and one for the LDC program in the US.
Corporations are set up because in order for an organization to get a bank account, own real property or do pretty much anything else a corporation has to be set up. It is solely a legal entity.
And btw no governing body member is an officer, agent or employee of any corporation.