> Rule 7: Don’t use leverage.

> Using margin accounts or mortgages (for other than your home) puts you at risk to lose more than your original investment.

As this says, margin accounts used in a certain way can put you at risk to lose more than your original investment. However, they are sometimes necessary to make investments with little to no additional risk. For example I may own $50,000 worth of XYZ Corp. and want to sell it on a Monday so as to buy $50,000 worth of DEF Corp on that same Monday. I can't do that if I don't have a margin account - settlement is usually T+2 days.

You can incur additional risk with a margin account, but not as much if it's just to borrow money you are almost certain you will have in a few days.