So why are these trusted deals needed? Why should somebody rent something if he/she doesn't have money for it?
And why people lease houses and cars? It's much easier to save enough money and buy them when you're ready... at the age of 60, for example =)
If serious - it's convenient. And profitable because of low price of transaction. You're not supposed to wait till the end of it, not supposed to bring fiat money, just a smart contract and you're free to do anything you want with your money