Checking in early—ideally as soon as the 24-hour window opens—is critical for several logistical and comfort-related reasons. First, it allows you to secure your preferred seat (such as an aisle or window) before they are snatched up by other passengers. For airlines that do not assign seats in advance, like Southwest, checking in early determines your boarding position, which directly impacts your access to overhead bin space. Second, many airlines use check-in times as a tie-breaker for complimentary upgrades or standby lists; the earlier you check in, the higher you rank. Third, it serves as a safety net; if a flight is overbooked, the last people to check in are often the first to be "bumped" or moved to a different flight. In 2026, mobile check-in also saves time at the airport, allowing you to head straight to security or a self-service bag drop, significantly reducing the stress of navigating crowded terminals.