Will allow you to buy up to $7500 of shares (speccies) not on their popular list and up to $15,000 might be 25k for blue chips (cant remember) with no funds.
If you own stocks registered under commsec chess, then add the value of your portfolio to those limits.
In other words if you have a 100k portfolio.
you can buy 107500 and 115000 worth of stock repectively without money in your account.
as long as you sell that day or next day or sell other stocks in your holding that day or next day for the same or greater value, you dont actually need the funds.
Can be good and bad. Trading haults or fast depreciation of stocks can sting you if you only intend holding for 1 day.