Apple has turned file saving on its head in macOS. You cannot save a file any more. You need to be aware of this, or you may constantly cause yourself problems, not only in Rhino, but in other applications too.
This information applies to all applications that implement macOS's Auto Save and Versions.
The following paragraph was in a recent Rhino for Mac release note. If you have not read the article, you should do that now. You should also read all the other articles referenced in the URL.
More information about Versions and Auto Save specific to Rhino: http://wiki.mcneel.com/rhino/mac/autosaving/.
Everything below is also stated in the articles. We merely state it much more bluntly here.
Auto Save does not mean autosaving
On OS X prior to Lion and on Windows computers, the term autosaving meant writing a single backup copy of your file somewhere else that you or the program can find later. The term autosaving has meant this for a long time. You were responsible for saving your file regularly, but Rhino and other programs created a backup file just in case you forgot to save your file.
In macOS, Apple unfortunately uses almost the same term, Auto Save, to describe something entirely different. In macOS, Auto Save means saving your file automatically – as in, overwriting your file automatically. As in, there is no secret backup somewhere else. Your original file is getting overwritten. All the time.
How often is a file saved? All the time.
This is how Apple describes it:
Auto Save in macOS saves during pauses in your work and, if you work continuously, it will save after 5 minutes.
Try the following experiment:
Within 10-20 seconds, the preview image of your file icon on the Desktop will change to match the Perspective view of your model. Select the Rhino file on the Desktop and select File > Get Info in the Finder menu. You will see that the file modification date has changed. Your file has been updated on the disk.
The same thing happens when you switch from Rhino to another application. macOS Auto Save will save your file immediately when you switch to another application. In the experiment above, instead of doing nothing for 10-20 seconds, switch to the Finder. Your file is immediately updated.
Also, your model is saved when you close the model window or quit Rhino. You will never see a Do you want to save your changes? dialog.
There are safeguards that are custom to each application to ensure that Auto Save does not happen while you are modifying the model. Each copy written to disk is an accurate and consistent copy of your model at the time it is written. For example, Rhino will never perform an Auto Save when you are in the middle of a command. Rhino also creates a snapshot of your model in memory and then writes the snapshot to disk. The writing to disk is done on a background thread, so even if your model is stored on a slow network drive, the Auto Save will not block you from working while waiting for your model to be written.
You can no longer save a file
More accurately, you cannot decide when your model will be saved on a disk. The system is doing it for you, and does so all the time. You cannot save a file, because it has already been saved for you.
Apple's goal is two-fold. One, what you see on the screen is what is stored on the disk. You no longer have two versions of your model: the last saved version on disk and the currently modified version in the Rhino application. Now, they are one. Two, you are much less likely to lose work because of a crashed program or a crashed operating system.
Command-S does not mean Save A File
If you type Command-S all the time to save your model, this is now a bad habit, because Command-S no longer saves a file. It does something entirely different, and it is probably not what you want.
Open one of your models and look in Rhino's File menu. The Save menu choice is no longer there. Instead, Command-S is associated with the new menu choice Save A Version. When you Save a Version, you create the equivalent of a Time Machine backup of your file. This is a backup copy of your model that you can retrieve any time. Also, even if you never explicitly Save A Version, the system automatically creates versions for you, approximately one an hour. These are also backup copies that you can retrieve in the future.
Each separate version that you save is retained by the system. Creating a new version does not overwrite previous versions but instead adds to your collection of versions.
Every time you type Command-S, you add another Version to your file. Pressing Command-S a lot means you create a lot of versions of your file. You probably do not need or want all those distinct backups in the future. You should instead stop typing Command-S all the time if you just want to save your model. This is no longer necessary. The system is already saving your model for you.
The system also provides a Time Machine-like interface to look at these saved versions. Navigate to the File > Revert To menu. Choose Browse all versions and macOS will present you with a browser to view all the past saved versions. Command-S does not save your file to disk. Instead, it is doing much more work by creating a backup, a duplicate, and browsable version of your file.
If you are working on a new model and have never saved it, then typing Command-S brings up the standard File Save dialog (just as it did before) and you pick where to store your model. But after this initial save, the system will decide when to save your model.
IncrementalSave is gone
If you are used to using Rhino's Incremental Save, Versions provides a built-in replacement that has a much better user interface. In fact, Incremental Save interferes with OS X Lion's Versions because it is constantly changing the file name of the model, so Incremental Save is no longer available as a command in OS X.
OS X Mountain Lion (10.8) changes
Apple made some additional changes to Auto Save in OS X Mountain Lion (10.8).
In 10.8, Apple changed the File > Save A Version menu title back to File > Save. But, the behavior is still as described above. File > Save on OS X 10.8 archives a version of your model along with writing the model to disk.
Starting with OS X Lion, any standard OS X application has a File > Duplicate menu choice. This opens another document with a copy of the contents of the current document. To save a copy of your model, you needed to duplicate it first, then same the duplicated model with a new name. Starting with 10.8, when you hold down the Option key, the File > Duplicate menu choice menu choice changes to File > Save As… and you can save a copy of your current document directly to disk with a new name in a single step.
Auto Save constantly saves to disk any changes you make to a model. If you wanted to experiment with a model and then close the model without saving any of the changes, Auto Save in 10.7 made that difficult. If you just closed the model, all the current changes would be automatically saved to disk by Auto Save. You had to explicitly revert your model back to a previous version to undo your changes.
In 10.8, there is a new setting in System Preferences > General for changing that behavior. There is a checkbox titled Ask to keep changes when closing documents. We suggest that you check this checkbox. Now when you make changes to a model and do not explicitly save your changes before closing the model, the system will ask if you want to save your changes. The Don't Save button lets you discard any changes that you made to the model since your last save. Note that this is a system-wide setting and will change the behavior of all programs, not just Rhino.
As you work on a model, there are natural break points or phases in your work. These are good places to use Save A Version to take a snapshot of your work so far. Remember that the system will make regular snapshots of your model about once an hour, so you will have many recovery points if you ever need to go back and retrieve previous work.
Apple has fundamentally changed how we are used to working with our documents. There no longer is a distinction between what we see on the screen and what is stored on the disk. They are always kept in sync. It is going to take some new habits and retraining ourselves to adapt. It is also going to be a rocky transition as some applications are converted to Auto Save and Versions, while others are still using the previous File > Save paradigm. We must remember how to work with both programs until all programs have made the transition to Auto Save and Versions.