When is it better to borrow against portfolio vs selling vs normal loan?

I have been trying to research how to maximize investments and options and the one thing I feel I can’t quite get a grasp on is when to borrow against portfolio vs selling vs a “normal” bank loan.

Where I am in understanding - selling your“portfolio” has taxes based on taxable income. So the more taxable income you have, the more the tax burden is on long term capital gains, up to a certain percentage (~37%). That said, borrowing against said portfolio comes with interest, slightly higher than a normal 30 yr, but without paying taxes on the sale. Either loan option though, your left paying interest vs cash up front.

Question - how does it actually benefit you to borrow against your assets if you don’t have an income? Additionally, can I borrow and just default on the loan and “give up” the collateral? What benefit is it to borrow at a higher rate against my portfolio than a normal 30 yr fixed rate mortgage?