> Explaining necessary details makes the difference between good or bad storytelling.

Only when the details you are explaining are relevant to the story you want to tell and the themes you want to cover.

In The Left Hand of Darkness, Le Guin explores a planet populated by an offshoot of humans who have developed a genderless existence where they experience sexual characteristics only once a month and are genderless the rest of the time.

The book does not explain how this works biologically or why this came about evolutionarily, because that is not the point. The interest of the author was to explore the cultural and sociological implications of this situation. If a group of humans lived without gender most of the time, how would this affect their culture and society? And what does that in turn say about our own gendered society?

Diving into the biological nitty-gritty of this fictional scenario would distract from the social themes the author was trying to explore.