Tether is a fully centralized system, tokens can be frozen or confiscated.

Tether is a fully centralized system that is merely recorded on a blockchain. Your tokens can be frozen or confiscated by a central group of people that control Tether. They could wipe out all profits kept in Tether in one action.

SOURCE: https://www.reddit.com/r/CryptoCurrency/comments/cq82hw/if_you_keep_your_traders_profit_in_tether_just/