When checking this option the data from the demographic will apply to all household members and should only be used for details that are the same for all household members. For example, "Gender" is unique to each person in the household, so you would NOT want to check this box. Whereas "Residential Status" applies to all people living together so this "Household Demographic" feature can be used. Please note that if this demographic is updated in the future it will update for all household members as well.

(see screenshot here).