Actually, the $10 is for early check-in not early boarding. Granted, the ability to check-in 36 hours prior to departure rather than 24 hours does give you a better chance of being in A16-A30, but it may only get you a low number in Group B. Business Select (A1-A15) and Rapid Rewards A-list also get 36 hour checkin automatically.
By the way, families with children board after all of A group has boarded anyway; so, this won't affect them.
