2-23. Regardless of mission, every Army staff has common broad areas of expertise that determine how the commander divides duties and responsibilities. The duties and responsibilities inherent in an area of expertise are called functional responsibilities. Grouping related activities allows an effective span of control and unity of effort. Areas of expertise may vary slightly, depending on the echelon of command and mission. For example, at battalion level there is no financial manager, while certain sustainment units combine the intelligence and operations functions.