(i) Unitary government has only one level of government whereas a federal government has two or more levels of government.
(ii) In unitary government, the sub-units are subordinate to the centre, whereas in a federation, central government cannot encroach on the rights of state governments.
(iii) In unitary system, centre can order the sub-units which cannot happen in federation.
A federation is preferred because:
(i) It helps in making administration effective and efficient.
(ii) It helps to accommodate all diverse groups.