[pre]

You borrow some money, buy a house, do it up, sell it for more, pay off the debt with some left over for your trouble.

That's using debt as a tool to make more money than you could have made if you didn't have access to credit to buy the house.

Or you borrow some money, build a car-factory, sell some cars, pay off the debt, and then have an income stream you couldn't have had without having access to credit to pay to build the car-factory.