Auto Storage and Versions has been a feature of the Mac OS since OS X Lion was released in the summer of 2011. It is a long time for a very useful file versioning system to be available on Mac, but it remains largely overlooked.
If you are wondering which file version is and what it does, you are not alone. To understand its use, you must go back to previous Mac days. Back then it was not uncommon to lose a lot of work because an app crashed or the system crashed.
This fear of lost work convinced many Mac users to adopt a workflow that often saves work and save work in progress before performing any kind of system function, such as copying files, starting an app or downloading files.  Mac's bad old days are pretty old history, swept by bug fixes, better development practices, and features like auto storage and file editing.
Auto Storage and Versioning
Not all apps support file editing. In some cases, it's just because the app developer didn't choose to use the default file API provided by Apple, and instead rolled itself, probably because they needed some options not included in the original file manager. Or the developer's app would not work well with Auto Save and versioning because of the way it forces save without the user's request. Think about multimedia editing programs, where you don't want the changes you're working on to replace the original files until you're ready to commit to the changes.
For just about every other type of app, you automatically save and versions can ensure that you never lose a lot of work and allow you to return to previous versions of a document.
How to save automatically and versions
Auto Save and Versions are two parts of the file versioning system; You need both for the process to work. If an app is designed to support versions, it also supports automatic storage. File versioning is embedded in the file manager and is part of the document architecture that Apple offers. It is not part of Time Machine, nor is it dependent on Time Machine's feature or service. The two are often confused because the Version History viewer looks almost like the Time Machine interface. And while they both allow access to previous versions of a file, it's where their similarities diverge.
Versioning occurs when you create a new document in an app that supports the Auto Storage and Versioning feature. Once you have performed the original save or save as, the saved copy is saved as the current version. At this time, the app will automatically capture periodic still images of the open document and save them as a new current version. The older version is not lost; Instead, it becomes an earlier version.
Apps have a different way of ensuring that your work is automatically saved. While working actively on a document, if you take a break by not performing any tasks with the document, or moving the focus away from the document, saying to see a website, the app will take a new snapshot, create a new version of the document. In this way, an error, a freeze, or a crash on your Mac, or some of its apps, is unlikely to cause significant loss of work.
The last way an app can create a version is with the good old-fashioned Save command. You will still find Save in an apps file menu, along with the usual keyboard shortcut (Command + S). The only difference is that the app now creates a new current version and adds the version history.
All previous versions of a document can be accessed from the app and allow you to return to a previous version of a document. Did a bug in a document edit and have to go back to what was there a few hours ago? Automatic storage and versions make this a simple task. We look more closely at accessing the version history a bit, but first …
Duplicate or save as?
The change to Auto Storage and File Version caused a change in an Apps File menu with the addition of a Duplicate command and a change to when the Save As command is available.
You may notice that the older command saves that sometimes in the file menu, and some times not. Save which will be present in the file menu of most apps until you perform the original Save or Save As. Once the document is saved, the Save As command changes to Duplicate. Some apps completely release the Save As command and offer only the Save and Duplicate options in the File menu.
Duplicate creates a copy of the current version of the file in the same folder and adds the word "copy" to the File name. Then the My Document file will be My Document copy. The app's document window content is replaced with the copy, ready for you to work with (some apps open a new document window with the copy). Once the copied document is saved, a new set of file versions is created. The old versions remain with the original document and are not copied to the duplicate document.
Tip: Duplicate does not allow to save a file to a new format, which you can usually do with Save As command. If you need to change document formats, check if the app has an Export command, or try opening the File menu and holding down the Option key. The duplication command can be changed to Save As.
Access to Version History
Should you ever need access to a previous version of the current open document, you can do so from the app by selecting Reset to from the File menu. The Back to Command command will display a number of different submenus, depending on the state of the versions stored.
You will probably see:
Previously saved: Depending on the Mac OS version, it may be last saved. This will replace the current document with the last saved version.
Last opened: Replaces the document displayed with the version that was in effect when you last opened the document.
Browse All Versions: This opens the Version History viewer and lets you view all available versions of the document. If you have used Time Machine, the display interface will be very familiar.
You may not see all the submenus Return to; which are present depends on the state of the file versions of the current open document.
To use the Version History viewer, select the Repeat To option, browse all versions from the File menu.
The version history display will open full screen.
The left pane contains the current version of the document, while the right pane displays the last saved version. As in Time Machine, use the arrows on the right to return to previous versions. You can also use the time scale on the right side of the window to jump backwards in larger steps (hours, days, etc.).
When you find the version you want to use, click the Restore button to replace the current version with the one you selected.
Tip: You may not always want to replace the current version with the older one. Instead, you can restore the older version as a copy, essentially mimicking the duplicate feature. To make a copy, hold down the Option key; The Restore button will change to Restore a copy.
Tips within a tip: Documents in the Version History viewer cannot be edited (without restoring them), but you can copy text from any of the older document versions. Use standard text selection tools, such as dragging multiple words or lines of text, and then use the command + C keys to copy the text to the clipboard. You can then paste the text into other documents as needed.
You can also delete some of the older versions using the arrow keys or the time scale to select an older version. When the version you want to remove appears in the right pane, move the cursor to the top of the History View window. After a moment, the menu for the app you are using appears.
Select Reset, Delete this version from the File menu.
When you finish using the viewer, click or click the Done button.
What happens to the versions?
The file system maintains a database that keeps track of each document's file versions. Deleting a document from your Mac deletes all versions as well. This version will be deleted if you empty the Recycle Bin or use Terminal commands to delete a document.
In addition, versions will not follow documents you copy or move to another device, to iCloud or send as attachments.
Turning Off Auto Storage
Some habits die hard, so if you want to control when a document is stored, you can turn Auto Save Save System wide. This will not turn off the file versioning system, even if new versions are only added to a file when you manually perform a save.
To turn off auto save, start System Preferences by clicking or tapping the icon in the Dock, or selecting System Preferences from the Apple menu.
Select the General Preferences panel.
Check box in the Ask to keep changes check box when closing documents check box.
Although this option sounds like it only affects storing when quitting an app or closing a document, it also prevents an app from automatically storing a document.
You can close System Preferences.
To Turn off Auto Save again, just remove the checkmark you added above.
It's a package
Automatic storage and versions can be an older feature of the Mac OS, but it can help keep the time and effort you put into a document time well spent and not one lost effort should an app or mac crash while working.
But don't forget that file editing is not a backup. It cannot protect you from problems that may occur with the storage system. In a different way, backups and versions go hand in hand to ensure your work or play time is productive.