Production possibility
curve shows all the different attainable combinations of the production of two
commodities that can be produced in an economy with the given resources and
technology which are to be fully utilized.
Therefore, in order to utilize all the resources efficiently an economy must operate on PPC because all the points on PPC indicates production in which resources and technology are fully utilized. However, an economy may underutilise resources, whereby the economy will operate on a point inside the PPC.