It is estimated that there is about 1.3 trillion cash in US alone. If all of this was stacked one on top another, it is estimated that we could go half the distance to moon. Now imagine all the cash that is circulating around the globe. This is made even more acute with countries like Indonesia, Vietnam, Cambodia whose denominations are very small (in comparison to a dollar).
Each country also observes a discontinuation of smaller denominations owing to inflation. This along with replacement of old and torn notes. The amount of paper consumed by the cash printing industry is mind boggling. US currency alone needed about 1 million tons of paper for currency printing. With paperless payments, all the paper used to print currencies could be saved.