From a macro perspective, if these type of crypto were to become a significant presence in the financial system, their volatility could lead to losses, which could have implications for financial stability, especially if associated with leverage. Stablecoins are a different type of crypto and claim to offer conversion at a fixed rate to currencies such as the dollar or euro.
This seems to deal with the issue of extreme price volatility, given the link to underlying stable assets like the euro, and stablecoins could be useful from a payments perspective and as a medium of exchange. However, of course this means that they are only as good as the governance behind the promise of the backing.