INDIA, Dec. 10 -- An empty middle seat in your airplane row is a gift, especially when the hustle and bustle of the airport can make you feel like you're inside a pinball machine. When the cabin crew finally announces those magic words-"boarding complete"-and the seat next to you is left unfilled, you know you won't be bumping elbows with a stranger for the duration of your flight. Plus, you now have bonus real estate: more underseat storage, extra leg room, additional tray table space, a spare seatback pocket, and even another seat to put some miscellany, like the airplane pillow or your jacket. Or, do you?

Empty middle seat etiquette is a common thread on Reddit, with travelers speculating about what is fair when the space between you ...