The main reason I OLCI is that you never know (a) when traffic will be bad, when the train is delayed, or some other circumstances conspire to keep you from getting to the airport with that nice 1 hour cushion you thougt you'd have and (b) when there's some problem with your BP that will keep you from easily checking in. If you're going to have a problem, you want to have it at T-24 hours, not standing at a Chicken with 15 minutes to boarding, then getting a message you have to stand in line to see an agent.
Always, always, always OLCI.