This option decides if the LEX main window tree view panel is shown of not. So if you want to hide the directory tree view to have a more basic GUI view of the LEX, use this option (or the Expand/Collapse the directory tree panel button )
Another easy way to hide (and show again) the treeview panel is a special button on the left outer edge of the LEX window. It appears only when you move the mouse near the left window border:
When the tree view panel is invisible, you can move into a directory container by double-clicking on the regarding container object, you can change to the parent container of the current display container by pressing BACKSPACE or the Go up one level button .