[celticninja]

For every buyer there is a seller, bitfinex are not selling you the BTC. So that seller now wants to trade his USDT for USD to withdraw, whether he does that through bitfinex or another exchange using USDT, the end result should be an outflow of USD and a corresponding drop in the number of USDT.

[seppel]

Exactly, I'm wondering the same. Somebody bought 2.8 billion USDT and it is unclear who and why (to me).

[tripletao]

I think people hold USDT:

1. For convenience, like if they're speculating in BTCUSD and their exchange uses Tether.

2. Deliberately, because they're breaking the law and they'd get caught if they tried to deposit their money in a regulated institution.

I doubt many people in the first category have thought much about the risks, or even know the difference between USD and USDT--if they had, then they'd probably use a different exchange. I'll bet there's a lot of them, though. I could imagine that people in the second category would consider the risk and still want USDT. A portfolio of half each BTC and USDT is probably less risky in some sense than all BTC. Even if the investment in USDT has negative alpha, it might improve your portfolio's Sharpe ratio, if the correlation between the risk that USDT collapses and the price of Bitcoin is small enough.