Not always. Depends on how critical the components job is. For instance, going back to the nuclear power station, there's never one piece of equipment for a given function. Always at least two and in some cases three. Like the pumps that supply cooling water to the reactor. One can do the job but two are used to share the load (to increase reliability) and the third is on standby for a failure or if one is out of service for maintenance. This is an extreme example but the point is efficiency can take a backseat to reliability in some cases.
