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For example, if you are actively building and testing a complex application, it may be a good idea to periodically deploy (but not release) a stable build. In the notes, you can write "this is a checkpoint build as of [date and time] by [your name]". Now, if you continue app building and run into errors that you are unable to fix or pinpoint why they are happening, you always have this checkpoint build you can revert to. You can revert an application by clicking on the "Revert to this Version" button on the application deployment page as shown below:
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This will change your application (including all forms and application settings) back to the way it was when you created this checkpoint build.