It allows you to pay off an investment and a home loan through a single account. Interest on the investment repayments are tax deductible, but the home loan interest is not. This basically means you can pay off your home loan quicker, allowing the interest to gather on the investment loan, and deduct it from your annual tax. These are typified by:
Note that this type of loan has been under scrutiny by the ATO and without sound financial advise it may not be appropriate for you