In such cases, the value of their currencies is not very high in the global economy or in some cases such as Zimbabwe, are worthless to use for transactions. While some people in those countries just use trusted currencies such as the US Dollar as it is trusted by people worldwide, there is another alternative: cryptocurrency.
Considering that their currency is basically unusable, Zimbabwe has adopted cryptocurrencies as a means of trade especially after their banks wouldn’t allow them to make transactions using foreign currency. So far the use of cryptocurrencies there is rising and it probably won’t stop until they fix their economy. This shows that cryptocurrencies can help countries that have problems with their currency.
Another example would be Venezuela. As we know now, the region is rather unstable with their economy not doing so well, however, some of the people there are able to get by using cryptocurrencies which further proves that cryptocurrencies can greatly benefit places with economic difficulties.
Is it possible to buy crypto in those countries is a problem, I know many big exchanges like Binance and Bitmex don't allow opening in such countries.
I am giving out a few examples of exchange restricted countries. Better stock up some crypto earlier than later.
https://cointelegraph.com/news/binance-dex-will-geoblock-users-from-29-countries-including-the-us
https://www.fxempire.com/crypto/exchange/okex/review
https://www.cryptopolitan.com/bitmex-restricts-access-to-three-countries/
VPNs, Tor browser and other applications can all help you avoid these issues.