Using all the sample elements in all the selected clusters may be prohibitively expensive or unnecessary.
The technique is used frequently when a complete list of all members of the population does not exist and is inappropriate.
In some cases, several levels of cluster selection may be applied before the final sample elements are reached.
This method makes it unnecessary to create a list of every dwelling in the region and necessary only for selected blocks.
In remote areas, an additional stage of clustering is used, in order to reduce travel requirements.