At most (all?) exchanges you trade with currency that's already deposited at the exchange. So you can only create a buy/sell order if you gave them the coins t

At most (all?) exchanges you trade with currency that's already deposited at the exchange. So you can only create a buy/sell order if you gave them the coins to fulfill the order instantly. The current situation makes arbitrage less effective and slows down trade because it's more expensive to move bitcoins to an exchange though