Toggle Finder Toolbars

You can instantly shrink down the size of any Finder window by hiding its toolbar, sidebar and status bar. Just click on the small wide button at the very upper right of any Finder window. Click it again to show the bars. You can also use the menu View, Show Toolbar or View Hide Toolbar, or the keyboard shortcut Command+Option+T.
However, if you hold down the Command key and press the button you will instead cycle through various toolbar viewing options which affect all Finder windows.