Complexity is a separate issue from flatness of rate structures. Also, in the United States, income tax laws are often used by legislatures as policy instruments for encouraging numerous undertakings deemed socially useful — including the buying of life insurance, the funding of employee health care and pensions, the raising of children, home ownership, and the development of alternative energy sources and increased investment in conventional energy. Special tax provisions granted for any purpose increase complexity, irrespective of the system's flatness or lack thereof.