I've found it extremely useful. I did both Business Studies and Economics for HSC and so far i've found:
1. I knew basic balance sheets/profit and loss statements and their components - accounting
2. I knew the basic performance ratios such as Debt:Equity, ROE, etc, and how to evaluate them - accounting again
3. I knew the theory behind debt/equity and the advantages/disadvantages - accounting
3. I knew most of the economics stuff (both macro and micro) - that includes balance of payments, exchange rate theory, demand/supply curves and how they're constructed/how they move, elasticity, etc etc.
That's all I can think of right now.
Basically, it ensures that you're not thrown into the deep end and allows you to bludge the first year a lot more. First year Commerce basically takes a lot of the stuff you learn in HSC BS and Eco and builds on them exponentially, but the ground work is great to have.