In which type of government does a local government exist only to assist the central government

In UNITARY GOVERNMENT, a local government exist only to assist the central government. 
A unitary government is one in which a state is governed as a single power and the central government is considered as ultimately supreme. Every administrative division in this type of government exist only to carry out the functions delegated to them by the central government. Most of the states in the world practice this form of government.