I know you know this.  Or you should know this.  If you have access to the Internet and a printer and you’re traveling, you really should check in with your airline — up to 24 hours in advance of your flight — online.  Most airlines will even issue you a boarding pass.Advance check-in can help you avoid lines.  Like, lines for people without boarding passes.  You also get to select your seat when you get your boarding pass at home.  This could put you ahead of most of the schleppers at the airport who neglected to do this.  You arrive with your bar-coded boarding pass and glide right by.Checking in online makes you seem more savvy to the airline employees and believe me, they will show some serious respect.  Well, they might not show it, but it’s there.  Deep down.  Know it.