We always checkin 24 hours before with SW and then use curbside checkin at the airport....sometimes there may be a small line, but, I've never waited more than 5 minutes. One thing to keep in mind, however, SW does not have assigned seating at all. They use a Line A, B, C concept so if it's important to you that everyone in your party sit together (if you are traveling with a larger group....usually two or four people sitting together is not a problem) it's important that you do check in 24 hours prior to your flight as that's how you are assigned a line .....Line A's board first and so on. A lot of people don't like this system, but, I actually prefer it because YOU can choose where you want to sit as you board...for instance, I'm sure we've all at some time thought to ourselves while waiting for a flight "Gee, I hope that person or family isn't sitting near me" for whatever reason.....talking loudly, unruly children, already spent too much time in the airport bar, etc. With assigned seating you don't have that option.....