I think this is the general gist of "only pay cash".
Debt is a tool. It can be a very useful one. It can also be very dangerous when used inappropriately.
Buying a car is a great example. Some people will say to only ever pay cash. But if you're eligible for a 0% financing promo, you'd be stupid to pay cash because you could invest that pile of cash and (almost guaranteed) make money at the end of the term. And some people will still prefer to pay cash because then the deal is done and they dont have to worry about a payment at all, which i totally understand.
I paid cash for the roof on my house. But i got a 0% down for 6 months home improvement loan to install a new HVAC system because the local utility operator is offering a $12k rebate. And when i receive the rebate check, I'll instantly pay off the loan.