Not sure what this feature is used for. It seems like it is impossible to use.
I would like to save any data entered into the field when shown, in case they accidentally hide them momentarily. However if I try to use this feature it is impossible to submit the form, since it says that all the fields are required, even when they are not shown. You can't fill out fields that are hidden. It wants you to fill them out regardless of them ever even being shown.