Money comes in all sorts of forms from cash, to checks, to debit cards, and to all the other representations of money that are commonly used in electronic transactions. When it comes to money, the actual amount of cash that is physically printed is a very small subset of the amount of money that is circulating around the world. Additionally, money, for the most part, doesn't recognize borders, so American dollars aren't just for use for people in the United States, but are actually in many instances commonly accepted as currency worldwide, and typically is the currency that all other currencies issued by other countries, are measured by.
In general, people are somewhat familiar, that in today's world, the value of a given currency, actually fluctuates, in which Americans most noticeably can see that fluctuation by comparing the value of the American dollar vs. the Canadian dollar or the Mexican peso. What most people don't seem to recognize, is not only does currency fluctuate, but in actuality, banks and other institutions, speculate in literally billions of dollars every day in regards to currencies, and bet big money as to whether a particular currency is going to go up or to go down in value.
The thing about the speculation on money, is that such speculation, in and of itself, as a way to "make" or to "earn" money is not only a zero-sum game, in which some will be losers and some will be winners, but it doesn't actually add to any nation's productivity, although it does so make a material difference to those banks and institutions that are speculating on currency. For instance, as reported by, theguardian.com, "… in 2011 only 0.6% of foreign exchange could be traced to genuine international trade in goods and services. Of the rest, a minimum of 80% was directly attributable to exchange rate speculation."
The problem with all of this speculation, is that enormous resources, analytics, and algorithms, are utilized in order to benefit from speculation for that particular institution's trading desk, at the expense of those that are either unable to compete at what is often a currency game that favors certain players, but also at the expense of nations, that are at the mercy of the currency speculation game in which these typically much smaller countries do not have the capacity to prop up their currencies, or to protect their currencies, or even to stabilize their currencies, and ultimately lack the ability to opt out of having their currency being speculated upon.
Another problem with currency speculation as done at the level and size it is performed at today, is that rather than seeing this currency trading as inherently keeping currencies within nations at a fair market value, it instead, creates a measurable increase in the velocity of how much a given currency within a country, moves up or down in value, which is clearly destabilizing. Additionally, all sustainable businesses, in order to make correct business decisions, need to be able to forecast reasonably correctly things such as future interest rates, the value of their currency, and the value of their debt; because if the value of the currency that is being utilized, has significant movement and volatility in either direction, this again, is destabilizing to those businesses.
Finally, currency speculation in a nutshell, favors the few, powerful and connected, at the expense of the many, in which not only is it a game of exploitation, but it also utilizes considerable financial resources for something that produces nothing of value for the people as a whole. In point of fact, this excessive worldwide currency speculation is a tinderbox to worldwide currency stability, so that, without change, it will eventually implode with devastating human consequences.