Well it depends. Although you can't buy a service or a product with crypto currency, it is still valuable in a sense that you can exchange it for Fiat that could be exchanged for goods and services. Therefore it would still hold value because it could stil be exchanged into something of worth. Then again, different people percieve worth.
Bitcoin is a transaction that occurs digitally on the internet, so it must be exchanged first in place to exchange bitcoin into fiat money, so that it can be used to buy any goods and services. This happens in a country that prohibits the use of bitcoin for payments. If it occurs in a country that legalizes bitcoin, transactions can occur directly from the transfer of the sender's wallet to the recipient's wallet.