The problems are that this is 1) hard to use for arithmetic, and 2) brittle.<p>"Brittle" because you're peacefully sitting there at 9999 coins or whatever, and you earn another one, and suddenly you can't represent it. Arabic (Hindu) numerals just slap another digit to the left, but Cistercian numerals break.<p>(You could fix that by using an Arabic notation - two Cistercian numbers, with the left one meaning "multiply this by 10,000". At that point, Cistercian numbers become a compressed Arabic notation. Still harder to use for arithmetic, but that's true of many compressed formats.)