According to the chronicler, the Levites helped out by getting food ready for the priests because the priests were busy all day making special offerings to God. This way, everyone could have their food and still do their important work for God.
2 Chronicles 35:14: And afterward they made ready for themselves, and for the priests: because the priests the sons of Aaron [were busied] in offering of burnt offerings and the fat until night; therefore the Levites prepared for themselves, and for the priests the sons of Aaron.
Leviticus 7:33 outlines that the priest who offers the sacrifice should eat it, whereas 2 Chronicles 35:14 describes the Levites preparing the offerings for everyone else, permitting priests to concentrate on the altar duties.
Leviticus 7:33: He among the sons of Aaron, that offereth the blood of the peace offerings, and the fat, shall have the right shoulder for [his] part.