Hi,
When I drag a movie from my photos to create a project in Movie, does the computer now have 2 movies in 2 locations?
Yes. One full sized copy of the movie is located in the original media folder in the iMovie library. So it would be located on whatever drive that your iMovie library is located, whether that be your internal drive or an external drive. Thus, people frequently store their iMovie library on an external drive so that the imported source files do not take up space on their Mac's internal drive.
The other movie file remains located as a full sized file where the source media was originally located. In your case that would be on whatever drive on which the Photos app is located. So, if your source media were located on an external drive, then your source files would remain there. If you had imported your movie files to a Finder folder on your Mac before importing into iMovie, then the movie files would remain located on your Mac. Thus it is possible that there could be two full sized duplicates on your Mac in the event both your iMovie library and your source file folder both were located on your Mac.
And when I save that project to a movie, do I then have a third version?
That is correct. A shared (exported) project is an independent movie. It would take up space on whatever destination drive to which you sent it. The source files and the movie files located in the iMovie library original media folder would remain intact.
If I deleted the project and the original movie, could I still use the Movie I've created in a new project?
Yes. A shared out (exported) iMovie project creates an independent movie file with all of the original clips merged into one long clip. You could fully delete the original project and source media. (You would need to delete the project plus the event that contains the media in order to fully delete the project. ) Then you could import the newly created movie into a new iMovie project. Because the original clips are merged all together, they would have lost their identitees as separate clip segments. So by deleting your original source files you would no longer have them as source files in their original form. The embedded edits in your exported iMovie project movie that you previously made could not be changed. You could edit the long exported movie to a limited extent, such as splitting it into segments, trimming it, deleting the segments, adding additional effects, adding titles, and adding additional clips. You could not recover previously trimmed out footage.
I want to pare down my files and don't want to keep multiple copies.\
Saving space is a concern, of course. The best way to do that is to purchase an external drive where you can store your data outside of your Mac's internal drive. If you store your iMovie library on it, you must format the external drive Mac OS Extended (Journaled) or APFS before moving your library to it. Formatting can be done with the Disk Utility app located in Applications/Utilities.
-- Rich
