Borrowed capital can amplify investment returns. If you invest £1,000 and see a 10% return, you will receive £100 in profit. If you leverage your investment by borrowing £9,000 to add to your existing £1,000, you will have £10,000 to invest and that same 10% return will yield £1,000.
However, because 90% of what you have invested is borrowed, the return on your initial £1,000 is 100%. Leveraging has enabled you to double your money (excluding borrowing costs).