Checking in for your American Airlines flight exactly 24 hours before departure is highly beneficial, even though it doesn't dictate your boarding group as strictly as it does on Southwest. For passengers without elite status or those traveling on Basic Economy, checking in early can be the difference between securing a preferred seat and being assigned a middle seat near the lavatory. If the flight is overbooked, American typically prioritizes passengers who checked in first when determining who gets bumped. Furthermore, if you are hoping for a complimentary elite upgrade or a paid "last-minute" upgrade, your position on the standby list is often influenced by your check-in time. For international travelers, early check-in allows the airline to verify your travel documents (like your passport or visa) via the app, which can save significant time at the airport and ensure you aren't flagged for manual verification at the gate during the boarding process.