Developers set Visible to False when they want to hide a button from the end user temporarily. The TBarButton continues to maintain its state on the server-side (if EnableViewState is True on the toolbar element). On subsequent postbacks, developers can un-hide the button to show it again.
A hidden button renders no HTML to the browser, therefore its position in the rendered toolbar will collapse (this may affect the layout of other buttons unless accounted for separately). Although the button's state persists through viewstate, it is not accessible to client-side script.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2