While rarely "mandatory" in a strictly legal sense, web check-in has become a functional necessity for the modern traveler in 2026. Most airlines now allow you to check in via their app or website 24 to 48 hours before departure. Doing so allows you to confirm your seat, pay for baggage at a discounted rate, and receive a digital boarding pass. For many budget carriers, failing to check in online can actually result in a "manual check-in fee" at the airport counter, which can range from $20 to $50. Furthermore, checking in early increases your chances of getting a better seat if you haven't pre-purchased one. Even if you have bags to drop, having already completed the web check-in allows you to use the "Baggage Drop" kiosks, which typically have much shorter lines than the full-service counters. In short, while you can still show up and check in at the desk, doing so is increasingly time-consuming and potentially expensive.