Tether is useful for traders who wish to stay "flat" with their positions for some time as it's the best instrument to instantly cash out for USD on crypto exchanges while keeping your money on the exchange. However I think you shouldn't hold them for long because there have been some issues with USDT when the Dollar peg didn't hold and the company is not really transparent about their reserves and how they were able to double their balance sheet in this short period etc. So stay cautious.