A unitary state keeps all power under the control of the central government, while a federal state splits power between central authorities and local or regional governments. Typically, a federal state has a constitution or other supreme law of the land that outlines the powers granted to both the central and local governments. The United States is an example of a federal state.
Each of these systems has various advantages and disadvantages. A federal state often finds that it is duplicating services, with certain agencies of the federal and local governments performing similar functions. In a federal state, citizens in different parts of the country are subject to different laws as well. On the other hand, federal states give citizens a much greater say in local matters than unitary states.
Unitary governments possess the advantage of having laws that are uniform throughout the country. They also face fewer problems regarding duplication of services and are able to avoid conflicts with the central government and local officials. The main disadvantages of a unitary government are that local authorities have no power to pass their own laws to deal with local problems and the central government is often slow to respond to local needs.