When you borrow money, the bank makes sure that they take a form of security from you in order to ensure that their money is safe. In the case of margin lending, the security that the bank accepts is the shares themselves or the investment that you are making. Those who consider margin lending to be a good option feel that the maximum that you stand to lose is the amount of money that you have put into the stock purchase.
Margin lending therefore allows you to purchase some of the blue chip stocks that you would otherwise have never been able to purchase in the first place. This kind of an option is used immensely when a popular blue chip company is offering an IPO. Retail investors generally purchase the stocks with margin lending at a price and then when the rate shoots up on the opening day, part of the shares are sold off to pay back the loan immediately.
It should however, not be forgotten that margin lending can be risky business. The manner in which shares move can be so rapid that you may not realize before you lose out on all the amount that you have invested.