Thank you OP for asking, as it is something that I don't really understand either. If airlines will have an option to automatically check you in, (which seems far from uncommon these days) what is the point of it in the first place? Why does it need to be a different function from purchasing the ticket/reservation? Especially considering earliest check-in times can range from 2 hours (when you have to check in at airport) to 60 days, at that point, what is the purpose of it as an additional step?