Maybe I'm not explaining myself correctly.
I can take crypto (and I'm talking about BTC/ETH, but can be others) and lend it out (generally for a positive APY). I can then borrow (typically USD*, but can be many other tokens) against that collateral (sometimes even for a positive APY!).
No permission needed and happens in the scope of transactions that cost pennies.
This is a massively important aspect of finance that goes beyond daily price swings. It is a relatively new aspect in crypto that has only been around for the last ~3 years or so.
Example: https://aave.com/ ($8.2b locked up right now)