Sidebar Autohide
Whenever you "touch" the left side of the content area with your mouse cursor (without hovering over the window border!) and stay there for a brief moment, the sidebar pops up. If you enter the content area again, the sidebar will disappear. You can configure both the sensitivity in pixels and the delay before the sidebar appears.
If you want the sidebar to stay open, either leave it by going up to the toolbar first, or click the sidebar's right border before entering the content area. The next time you leave the sidebar the normal way, it will disappear again.
You can also temporarily lock the sidebar by clicking the "hand" button. While it is locked that way, the sidebar will not automatically close - however, if you close it manually, it will still open automatically when you touch the left window border.