Why doesn a maximized window occupy the entire display?
The sawfish window manager restricts the dimensions of maximized windows so that they will not conceal the default GNOME panel (the edge panel at the bottom of the screen) and the menu panel at the top of the screen. If you want more space for your maximized windows, you can remove the menu panel and/or modify the default GNOME panel to automatically “hide” until the cursor reaches the edge where the panel resides.