A not very degen version of this is taking money that you might spend on your mortgage at a rate under 3%, and putting it somewhere safe that earns more than 5% (not hard to find).
I already owned the house free and clear. Was offered stupid (good) terms for a mortgage so I took it. Used the money to create a return that pays back the monthly interest and principle while still creating a return AND tax deduction.
How do you use the leverage (debt) from the mortgage to put in a 5% investment?