Ive not done it not with air france so it may be very different, but we always check in online (if its available to do). Last year when we went to Florida and we checked in online it mean that the 9 of us all going together were all seated together in a few rows. I say its definatly worth it, it also means all you have to do at the aiport is check your lugage in!
You may want to check what the benefits are of checking in online with air france though.