When a building is constructed from standard parts that have been well tested ____ .

The practical advantages of prefabrication are twofold:
It is quicker and it does away with uncertainty.
Speed in building is important in these days because
of the high cost of land: the time during which such an
expensive commodity is out of use must be reduced to
a minimum. And, partly or wholly prefabricated
methods of construction save time on the job because
parts are prepared in the factory beforehand.
Prefabrication does away with uncertainty because it
means that the whole building is made of standard
parts the behaviour of which is known and has been
tested.