Why effective public services need spare capacity

Armed forces and public services need spare capacity to cope with disruptions. A system operating at its limit can become ineffective as soon as something unexpected happens. Schools provide a concrete example: spare places elsewhere in a county allow pupils to continue their education if a school suffers a fire. Those unused places cost money during normal operations but provide insurance against an emergency. The same reasoning applies to hospitals and emergency services, where efficiency must include the ability to absorb disruption.