And if the "maximum bag" which is within CAA limits is put in the hold at the gate, it is carried for free?
Yup. No charge if its within the 'max' limits.
This new 'rule' in reality means absolutely nothing is changing, other than people who have a bag under a certain size are now guaranteed not to have it taken away from them.
Lots of bags on every flight have been put in the hold, free of charge, for quite a long time now and this is just a way of giving people the option of knowing 100% that they can keep their stuff with them.
Hopefully it will mean less arguments at the gate.