If you are taking a flight, make sure to check in on-line, and do it early. You can usually check in starting 24 hours before your flight. If you check in on-line as early as possible, you'll get a much better seat assignment than if you wait for later or check in at the airport. Some people think that if you are checking in bags, you can't check in on-line or that it will make things harder. This is not the case. Almost every airline now has a special line for people to check in bags after they have checked in on-line. If you want the best possible seat on your flight, checking in on-line is the best way to go.