Checking in is rarely done in person anymore. Checking in online is the norm, and I normally do it first thing in the morning, from home, wearing my bathrobe and sipping coffee. I don't know what practical purpose it serves for the airline, but for passengers it's just a formality you have to complete by a certain time to make sure they don't cancel your reservation. It has nothing to do with being at the airport on time, except that in this particular case I had to check in using my phone because I was in a cab on the way to catching my flight.