You could keep your exposure to the crypto. For instance you can sell 1 ether for 2500 DAI (haircut to the original value), move those DAI to a centralized exchange, sell for cash, do something with the cash, and eventually convert back to 2500 DAI and buy back your ether. Important thing is you kept exposure to the price of ether and didn't sell, just loaned it out. You can always buy it back at the price you collateralized it.

If the price went up since you took out the loan, you benefited. You're over collatralized so you'll always want to buy back, unless its below your collateralized value, in which case it would have been liquidated anyway

There are other aspects to defi other than lending, such as liquidity providing, governance token issuance, etc. For the loans part, you are right there is no use other than to speculate on crypto assets. An overcollaterallized loan is essentially just selling some coins for cash while simultaneously taking a leveraged long position to maintain your exposure.

If you noticed an arbitrage opportunity which required a substantial initial fund but could be executed as a single transaction, a flash loan could let you do that, and I think that’s kinda neat.

Seems like it should make some things more efficient? That is, if the things that the arbitrage is about have any actual meaning to them.