It makes sense to have some of your funds in euros or swiss francs, for diversification purposes. But keep in mind the transaction costs that you will incurr, especially if you want to trade often, or convert a few euros into dollars every month. The bid-ask spread is not negligible, and your financial institution will likely impose fees on top of that. There are fees for transferring money in and out of your account, plus fees for convertng foreign currency. And because of the bid-ask spread, you will start in the red (at a loss).
