[lawn]

With Tether you're essentially converting your cash into USD, but with massive risk added on top. Tether is, as stated by themselves, already not backed one-to-one by USD and you cannot actually redeem them, only trade them in exchanges.

What you instead should ask what effect real cryptocurrencies like Bitcoin can have.

I'm personally quite positive to cryptocurrencies, but I don't have a crystal ball. If a single country is about to go under of course it's a good alternative, but of the global economy tanks it's all up in the air.