The LastUsed workspace remembers the contents and coordinates of the workspace as they were when you closed NetObjects Fusion 12. It is saved only when exiting NetObjects Fusion 12; when you re-start Fusion, it will load the LastUsed workspace, as it was at the moment the program was closed.
When first installed, NetObjects Fusion 12 opens with the Advanced workspace by default. When exiting the program, the current configuration of panels and toolbars will be saved and kept as the LastUsed workspace and loaded as the new default the next time you launch NetObjects Fusion 12.