Residential structures

 are essential buildings for maintaining population. If a population goes over the number of available habitable space, surplus colonists are euthanized.

Strategy

 * It goes without saying that the two skyscrapers are the most efficient method of housing colonists. While they can extend commute distances, even the cheapest skyscraper offers a ratio of ~0.92 nanite per colonist, as opposed to a late-mode habitat's 1.09 nanite. However, it does consume ~0.47 power per colonist, while a habitat requires ~0.27 power.
 * Upgrading it to the Tier 2 model makes it a perfect choice across the board: 0.76 nanite and 0.28 power per colonist.