Is digital money good for the world economy?

Not at all

Digital currency is not backed by anyone or anything

Its totally worthless

Yes, everyone can create the money. How good it is? The invisible hand is working. Only when the market has problems, the losers must pay.

Thoeretically, it's just another type of currency, and it shouldn't have an effect on the macro economy one way or the other.

I can say that because of its anonymity, it has enabled new types of crime. For example cyber hackers who use ransomware and demand payment in untraceable bitcoin. 

that depends on who creates and distributes it, and how.

If it's just a toy for the rich it doesn't help ordinary people one bit

Yes, because it cuts through the ancient theory of gold standard or modern replacements such as stock market figures, and makes more possible the dream of sharing and caring for the poor nations through efforts to neutralize the classic diseases of corruption and violence.