Margin Trading allows people to trade on borrowed assets, usually for a short period. This is not for everybody obviously but I think it would attract a stream of people that are looking to make a profit with a low level of risk, namely the lenders of assets.
Basic use case:
Bob has 100 XML and he wants to buy USD because he thinks the price of XML relative to USD will appreciate. Bob is so confident that he is willing to borrow from Alice 400 XLM. Alice is willing to lend the XML to Bob because he promises to pay her back the 400 XML plus a small interest per day. Of course, Alice is not so sure that this will end in a happy ending for both of them, so she needs to make sure that if the exchange rate goes against Bob's expectations she still can close the deal and recover his money + interest accrued until that moment.
I was looking into Stellar Smart Contracts and maybe I'm wrong but don't think it's possible to do this with the current API. This use case presents a few challenges: how Bob and Alice will negotiate the daily interest? this is a market on itself. Or what's the maximum Leverage someone can get into? All good questions, few answers.