Quote Originally Posted by Risvertasashi View Post
Realistically a lot of family sharing (and even roommate sharing) happens and SE doesn't do anything to them. That clause is probably more for stopping things like powerlevelling services or otherwise paying someone to play your character.
It's also so SE can cover themselves if there is a dispute about the account. Such as a person's brother spending millions of gil buying a house the actual account owner didn't agree to, the brother deleting characters the account owner wanted to keep, or both people fighting over who actually owns the account. SE don't have to sort out personal disputes like this because the ToS specifically states one account is for one person.