Thanks to the single ledger and programmability, currencies could be exchanged simultaneously, so one party does not bear the risk of the other walking away. More generally, risk-sharing contracts can be written, auctions can support thinly traded currency markets, and limits on capital flows (which exist in many countries) can be automated.
Importantly, the platform would minimize risks inherent in such contracts. It would ensure that contracts be fully backed with escrowed money, automatically executed to avoid failed trades, and consistent with one another. For instance, a contract to receive a payment tomorrow could be pledged as collateral today, lowering costs of idle funds.
Beyond the transfer of value, encryption can help manage the transfer of information. For instance, the platform could check that participants comply with anti-money laundering requirements, but allow them to bid anonymously on the platform for, say, foreign exchange, while still seeing the aggregate balance between bids and asks.