Margin trading allows investors to borrow stablecoins or cryptocurrency to leverage their position and improve the expected return. For example, borrowing Tether (USDT) will allow one to buy Bitcoin (BTC), thus increasing their Bitcoin long position.
Investors can also borrow BTC to margin trade a short position, thus betting on price downside. This is why some analysts monitor the total lending amounts of Bitcoin and Tether to gain insight into whether investors are leaning bullish or bearish.