From what I hear, some people do this to get cash out of their crypto portfolio without a tax consequence. They put up ETH for example as collateral, borrow DAI, sell that for cash with no tax event. It gives them liquid cash and they get to keep their crypto which they expect to go up.

Or people leverage their existing crypto to buy more of it. Put up ETH for example to get DAI to buy more ETH.

I'm not an investment advisor or an accountant so this is for entertainment purposes only 😄

Not sure if this meets your criteria but its what came to mind.