As well as this, the dollar comes in a physical form. That adds another element of convenience when choosing to use it. The main downside to the dollars is the cut when exchanging to a different currency – as banks usually take a larger cut that they should do, thus decreasing the value of your trade. As well as this, through things like quantitative easing (i.e., printing money or adding it digitally to the banking system), the dollar could drop in value over time.