Truecauses the application to become iconified. Every open window will be closed and a (configurable) AppIcon will appear on the workbench.
Same thing happens when the user hits the iconify gadget in the window border or uses commodities Exchange to hide your applications interface.
When an application is iconified and you try to open a window, the window won't open immediately. Instead MUI remembers this action and opens the window once the application is uniconified again.