Efficiency - It is beyond the ability of the legislature to spell out everything necessary to protect the public health.

Flexibility - It is impossible to anticipate every threat to the public health.  Laws that try to specify emergency actions with detailed provisions often cause more problems in enforcement than laws with more general provisions.[Edward P. Richards and Katharine C. Rathbun, Review of the Model State Emergency Health Powers Act]

Speed - Public health threats demand quick action, which is impossible if you have to pass a law to address a new threat.