Purchasing power
The deviation in Purchasing power parity allows rural Indians to survive on an income below the absolute subsistence level in the rich world. If the money income levels are taken as given, then all else being equal the Penn effect is a very good thing. If it did not apply, millions of the world's poorest people would find that their income was below the survival threshold. However, the effect implies that the money income level disparity as measured by international exchange rates is an illusion, because these exchange rates only apply to traded goods, a small proportion of consumption.