These invented societies are frequently critiques of existing social norms and their possible futures as well as suggest possible solutions. Morality and ethics often are central to these critiques. Taken to extremes, social science fiction crosses into the utopia/dystopia genre.
Consider The Moon is a Harsh Mistress by Heinlein. The society on the moon has different mores concerning sex and marriage. The female to male ratio is very low. As a result, the society has introduced polyandry, the practice of a woman having multiple husbands, and group marriage, the practice of having shared spouses, both male and female, that often develops into line marriages which successively introduces new spouses so that the marriage does not end due to any one death. The family votes before a new husband or wife may join and the marriage is to the whole family. It also maintains economic stability by working from improvements made in the past and through multiple income earners. The continued line marriage also insures continual parental influence. This part of the novel is social critique. The romance and friendship of Manny and Wyoming is within the domain of soft science fiction.
Brave New World - Alduous Huxley
Nineteen Eighty-Four - Orsen Wells
Left Hand of Darkness - Ursula Le Guinn