Version History
"The Version History screen allows you to manage prior versions of the item being edited.
Each time you save the item with new changes, a new version is created automatically."
Source: Joomla! Documentation.
Default Version History Settings
The Version History functionality is controlled by the Behaviour - Versionable Plugin in the Joomla! CMS.
This plugin is enabled by default.
The default Version History setting for various elements in your website can be viewed when you select the Options button (see image) at the top right of your website's Dashboard.
Select the Options button in the Articles screen to see the default setting under the Editing Layout tab (see image below).
To turn off Version History functionality globally, deactivate the Behaviour - Versionable Plugin in the Plugins screen.
To do so locally (example: for Articles), toggle the button shown in the above image from Yes to No.