A couple of planet-related thoughts I've had over the years in the context of Science Fiction (movies, books, games, etc.)
1) Sometimes, in Science Fiction, something -- an artifact, a person, a dataprint -- will be lost (lost less in the sense of "I had it but dropped it" and more in the sense of "lost to the sands of time"). And where this is a plot point, the heroes usually will "find" the MacGuffin by figuring out what planet it's on (e.g., Luke Skywalker at the end of Episode VII).
I always found this rather striking. Imagine you're searching for a particular human being, and you're told "he's on Earth" ... and that being enough to go on. Even if there weren't a single other human being on the planet, Earth is still really big, at least from the perspective of finding a single guy. There's a ton more sleuthing you'd need to do! It's amazing to me how most "planets" are reducible to basically a square mile of (monolithic) terrain -- anything that's there, is there.
2) In any multiplanetary society, it is taken pretty much for granted that the smallest unit of practical governance is the planet. Sometimes it's larger than that (a galactic federation, or individual star systems), but there's virtually never subplanetary political divisions that are deemed salient on an interstellar level. "Earth" might have a representative on the Galactic Council, or the "Terran Federation" might, but "America" and "China" never do. That actually strikes me as more or less plausible, but it is interesting -- and it strikes me that if humanity ever does spread outside of our home planet we will rapidly coalesce into some form of global government -- at least for the purpose of managing space affairs.
3) Returning to the "planets are big" thing, you know what job must really be low-prestige in science fiction land? An "intraplanetary" transporter or military member. Imagine there exists Starfleet, and you're part of the Navy. Not the Space Navy, just the old-fashioned water Navy that protects ocean-going ships. Somebody has to do it -- again, planets are large and there will have to be substantial intraplanetary trade which will need protection from pirates or rescue from storms or whatnot. But goodness, imagine trying to pick someone up at a bar with that job -- working on a coast guard cutter when there are literal starships flying across the universe. That's rough.