Ann: Sale of Immersion Clinical Spas, page-76

If for example you dump and try to sell at 0.5c and someone has a Centerpeoint at 0.55c hiding you get paid the extra .05c... If you try to buy up at 0.7c and there are orders waiting at 0.65c you only have to pay 0.65c. Its makes for pleasant a pleasant surprise especially at these levels to get more than you expected for a sell (0.05c extra when willing to sell at 0.5c is 10%) or if you pay less when willing to buy up. Commsec will hit the Centerpoint trades for you, I'm not sure about other brokers.