The main problem with Fiat currency is that you need to use your Master card or visa card, meaning a lot of fees and long transaction time. With crypto, these issues dosent exist as you don't need to involve your bank in it. Not to mention that if you are from europe and you buy on japanese site, in addition to you the credit card fees you have to pya the money exchange. This is also solved with crypto as you can pay with the coin accepted by the seller (BTC for instance). Another very important thing, with blockchain technology you can track all transactions that happened on a coin and in some cases history is really important. Anyways, this is what I believe.