To be useful a chemical equation must be balanced what does this mean

Chemical equations need to be balanced in order to satisfy the law of conservation of matter, which states that in a closed system matter is neither created nor destroyed.

Thus, the mass of substances produced in a chemical reaction is always equal to the mass of reacting substances. Therefore, you need to have the same number of each type of element on each side of a chemical equation. This is the whole purpose of balancing a chemical equation.