such as in the book Skybreaker, chapter 8, Kenneth Oppel includes information (minor elements) such as George Barton and the Aruba Consortium, the possible presence of undiscovered creatures, the betrothal of Nadira, and Matt's desperate longing for money.
Would there even be a story without subplot? All relevant minor elements lend to the main plot and creates a believable fiction world for the reader. Often, they can AND do reinforce theme, tone, and symbolism throughout the story.