Bitcoin is good for countries economies because it is a fresh flux of investments if they are correctly regulated and directed.
I hope that one day Algeria will accept Bitcoin, it would be great for our economy and could help us solve a lot of problems due to the currencies change black market (3 bil EUR market cap) as people could buy Bitcoin and sell it in foreign countries instead of playing with the black market.
This was just an example of how bitcoin could help a countries economy, but i think that regarding the countries who aleready accepted it as a virtual currency, the main advantage is the security, as it is far better then using a credit card, and it can give a good punch to start-ups growth (if they are not scam)