Bitfinex is giving around 0.07% a day if you lend with Tether (usd) so it means that in ten days, you are going to make around 0.70% of your investment, it is a garbage
0.70 percent in ten days are not worth it, and you have to pay more than 15 percent of your earnings to the exchange. Poloniex is just taking 12 percent of those funds as fark as i know.
But lending tether is risky , because maybe bitcoin just makes a pump of 1% and you lost more money that what you have invested in that operation.
I dont know why there are some people who uses those systems to make some profit from them, because they all are in a huge lose after all.