语句return false的用处

  function winShow()//invoked by "开发票" 
       {           
          window.showModalDialog("invoice.aspx?id="+varHid2+"&inv_type="+document.form1.ddlInvoiceMode.value+"","","status:Modeless;edge:raised;unadorned:no;scroll=yes;resizable:yes;center=yes;help:no;dialogwidth:890px;dialogheight:620px");          
          return false;
       }

<asp:Button ID="btnToInvoice" runat="server" CssClass="btn2" OnClientClick="return winShow();"  Text="开发票"  />

关闭弹出的showModalDialog窗口后，本页面不刷新，所做的工作不会丢失，例如已选的要开的50条item，都还处于勾选状态！