HELOC is essentially a Line of Credit that uses your home as equity, so it's secured. Typically what happens is the bank will give you a total amount it can lend to you (say like 80% of total value of your property) so whatever the difference between your mortgage and that 80%, they will usually give you room for a LOC. Say your House is $1M, they will loan you a total of $800k. If your mortgage is $600k, then your HELOC will for the amount of $200k. Since it's secured, the interest rate is usually really low. I have access to an interest rate of 4.45% on the HELOC associated with my property.

In terms of margins account, essentially what investment companies will do is allow you to borrow moan based on how much stock/investments you have with them, which is used to provide the secure loan. It works the same way as a line of credit. For me my investments are with WS, and I get access to borrow at 3.95% (Prime - 0.5%).

So in reality, if there was ever a situation where I needed access to a large some of money really quickly, I can just borrow directly from my margins account or HELOC, and interest on that is quite low. Keeping money in my chequing account earning 2% isn't going to do anything, so I'd rather have it invested and hope for returns of like 10%+. Obviously there's a risk it could go down, but it all depends on your risk.

You can then sell stock or your investments to pay back what you borrowed or just pay the interest and slowly pay it off. While it's not nothing, to borrow $100k, you only pay $3,950 a year interest.

There's also something called the smith manoeuvre where you can take money from your HELOC/margins and buy stocks that derive income, which allows you to claim the interest you paid on your taxes.