I have read that that’s one of the wealthy’s “big secret” ways to avoid taxes. They allegedly live off of those loans as their spending money, while the value of the investments they use as collateral increases over time, but they don’t pay taxes on the Unrealized gains. And they can keep borrowing more as needed with those same investments as collateral.
I don’t have the whole scam figured out though. I’m not sure how they pay back the loans without having to cash out something that would generate a tax burden.