Last year, as a OWE (from AA EXP) traveling on a hand baggage only fare, I got an email the day before telling me that the flight would be full, and so that they recommend I check the bag for free.
When I checked in at F check-in, he said that I was on a Hand Baggage fare, and I mentioned the email. He asked to see it, but when I went to find it, the agent just checked the bag for me for free.