I think this is terrible advice for most people. You only need to spend like an hour in the airport to avoid missing a flight. Most people don’t fly often enough to get much actual gain from pushing this boundary. The only person I knew who would push the envelope like this was someone who flew every week for work. That makes sense to me, because you’re saving two hours every week for years. If you’re only flying a few times a year just pack a book and ensure you make your flight on time.