A. It's recommended to take a mortgage when buying a home, but for most investors, it's not a good idea to use a margin account to buy stocks/bonds/ETFs, for one key reason:
When you take a mortgage, the bank doesn't care much about how your house's value changes. Even if the house value decreases dramatically, as long as you are still paying mortgage on time, you are okay, the bank won't take back your home.
However, the same can't be said for when you use a margin account to buy stocks, bonds, or EFTs. Sure, you can use a margin account to buy stocks that are worth more than your cash value. However, if the stock's value drops, the brokerage house will force you to sell your investment, that's typically the worst time to sell.
In short, it's only recommended for advanced investors who could handle the risk associated with a margin account to buy investments with margin.