On the surface, I don't see a massive difference between home owners taking out loans, using their house as collateral. And using cash or crypto as collateral. Liquidity is the main difference, obviously. There is collateral with typical fiat loans, its only structured differently.
Another idea for how this could work.
Crypto used as collateral in a loan may not be as taxable an asset, as crypto held in typical capital gains scenarios. Your $1,000 in collateral could become free from taxation?
I would guess there is a loophole or angle somewhere that could make this worthwhile from a financial perspective. The only question is where.
On the investment side of things you are right, if you are going to make an investment there is absolutely nothing different at all, it is basically the same thing. However if you want to buy a house, you can't get a crypto loan because .. well you have to pay a collateral and get money which will not get you to a house.
In real world you have a salary, and you show your salary as a proof that you will pay it back, and you get let's say 100k loan and buy a house and pay your mortgage with your income without paying anything at all, you are out of zero amount from the start, you just pay it monthly, you can't do that in the crypto world with a crypto collateral.
However if you want to invest, this is about the same in fact I have seen multiple business loans the same way, there was a constructor who wanted to built a home, he put 3 million dollars into bank account, took out 9 million dollars loan, spent that 9 million dollars without touching his 3, built those big buildings and paid the loan back. Same stuff here as well.