Taking out a Scottrade margin loan increases your buying power by allowing you to purchase stocks on credit so you can buy and hold more positions. You can also use a portion as a ready source of cash. And, just because you open a margin account doesn't mean you have to use it. Once you're approved, your open line of credit is always ready and waiting in case you need it.
One of the risks when trading on margin is the risk of losing more money than you initially deposited into your account. If your account falls below Scottrade's maintenance requirement, Scottrade may require you to add additional funds to your account or may sell shares on your behalf to pay down your loan.