I've also thought about and discussed this topic at length.
Imagine being an early investor in crypto. The price spikes and now you have enough money to buy a house.
With security tokens, you could liquidate all your crypto to buy the house, but then use your house as collateral for a loan to get half of your crypto back.
As long as your house didn't lose half it's value you could keep both the crypto and the house while slowly paying off the loan.
You can already do this collateral based loan concept with Ethereum and MakerDAO. I've already done it multiple times. Once you figure it out it only takes a few minutes, and Ethereum is slow compared to the new up-and-comers. Also, it's much safer to use property as collateral than it is to use crypto due to extreme volatility differences.
The craziest thing about MakerDOA? The yearly interest rate is 0.5%!!! Not only that: this money gets destroyed; permanently increasing the value of Maker coins. Central banks don't stand a chance.