A characteristic of American government is the federalism that exists. Different levels of government provide different types of services. The benefit to local government is that it pushes democracy to the lowest level, where citizens can have maximum input. The same is true of law enforcement; a segment of government itself. A degree of this is lost with consolidation efforts. The first few pages of this report from Harvard Law explore federalism as it pertains to immigration enforcement, as an example: http://bit.ly/1dkIphA
What kinds of problems are presented by the layered system of criminal justice in the United States (federal, state, and local)?