It's typically better to check in online, since you can do so much sooner than you would be able to in person at the airport. As mentioned above, it's especially important to check in early for a Southwest flight, since boarding order is determined by check-in order.

While online check-in is not strictly mandatory for most full-service airlines in 2026, it is highly recommended as a standard travel practice. The primary benefit of online check-in—usually available 24 to 48 hours before departure—is that it allows you to confirm your attendance, choose or change your seat, and receive a digital boarding pass, which helps you bypass the long queues at the airport check-in counters. For those traveling with only a carry-on, you can often proceed directly to security. However, some ultra-low-cost carriers (such as Ryanair or certain regional budget airlines) may charge a significant "airport check-in fee" (sometimes as much as $50 or more) if you do not complete the process online beforehand. Furthermore, in some post-conflict or high-security regions, online check-in might not be available at all, as airlines are required to perform a physical document verification at the counter. For the best experience, you should check your airline's specific policy on their mobile app; if the option is available, doing it online saves time and often ensures you aren't the first person bumped if a flight is overbooked.