The characters in a novel have to earn the connections to their back story, otherwise, they risk coming off as cliche. A few overused and cliche characters are: 1) The nice guy who always finishes last. 2) The brooding bad-boy. 3) The trophy girlfriend. 4) The Anti-girl who is good at typically "guy" things without explanation.
When building a backstory, a writer should add intrigue and uncertainty. How will a character's template (the model learned from family and childhood associations) effect the present? Does the nice guy have a dark side? Is the bad boy faking it through life? Does the trophy girlfriend have substance to effect the plot line? How and why did they anti-girl become good at guy things and what happens to her personality if you put her in a dress?
Finally, what has the character learned from their parent's example and what do they expect, based on past relationships?
Sometimes it is convenient to add a character that fits a certain mold. Maybe you need a snapshot personality type to progress the story. They appear and are gone. But they can have more depth than what you've given them in their scene.
The solution comes in the main characters reactions to those cameos. A good example of this comes from the screenplay for Jurassic Park. The movie lasted 2 hours and 7 minutes, and there were only approximately 4 minutes of Dino cgi. The reason it feels like much more is due to the main character's set up and reactions. Through inference and conversation, the cgi on screen time is greatly enhanced.
In the same way, main characters can refer to the actions of drop-in cameo characters. A small bit character can have more impact than the writer had imagined. In this way, a writer can make every character memorable in their own way and give them more substance and relevance.
I hope this has helped. Thanks for reading.