There are certain Immigrant visas which do not utilize the I-864 as the affidavit of support requirement is waived. These type of cases require the submission of the I-864w. To quote the United States Citizenship and Immigration Service (USCIS) in their own instructions for the form itself:

“The Form I-864 is legally required for many family-based immigrants and some employment-based immigrants to show that they have adequate means of financial support and that they are not likely to become a public charge. Certain classes of immigrants are exempt from the I-864 requirement and therefore must file Form I-864W instead of Form I-864 or Form I-864EZ.”

Under the Child Citizenship Act of the year 2000, there are certain children who enter the United States and become United States Citizens by operation of law upon admission at a port of entry by the Customs and Border Protection Service (CBP). These children may then apply for a certificate of citizenship which is somewhat similar to a naturalization certificate except for the fact that the child is not naturalized, but a citizen statutorily. In cases where the child would become a citizen upon entry, the obligations incurred by an I-864 would automatically extinguish upon entry since the child would be a US Citizen. Therefore, the need to adjudicate means of support are made somewhat redundant. This may be the policy reason underlying the promulgation of the I-864w.