I store my movies and videos in double backed up finder folders, organized by year. That way I don't have them tied into any app that can become corrupt or obsolete. I can transfer them to other apps and computers easily. They are also much more easily retrieved for multiple types of uses. I import them into iMovie as needed. In the finder I can organize by sub folders such as Vacations, Holidays, Birthdays, Fishing, Date, etc.
I also have movies stored in the Photos app. iMovie can access them from the system photos app from the Photos item in the iMovie project sidebar. Clicking on the Photos item will display in the medica browser all of the photos albums. Since the photos and videos are only referenced until dragged into a project, they don't take up space on the Mac's hard drive, or clutter the iMovie library.
iMovie is a video editing app. While it does have some organizing capability, media management is not its strong suit. Storing unused media files there can be problematic at times. They are awkward to retrieve for other purposes. They slow the performance of the iMovie library. They can be lost if the iMovie library becomes corrupt or future iterations of iMovie change the basic architecture of the app. I find it safer and more convenient to keep a double backup of all my media in Finder folders that I can move around as needed. As mentioned, file retrieval is easier. And, better yet, the vids are not locked into some app where they can be lost.
As long as you have a Finder backup, the Photos app also is a good place to store video clips and movies. Photos has numerous file management tools, such as albums, smart albums, and keywords that allow searches and grouping. You can sort by subject matter, creation date, date added. iMovie doesn't have those capabilities, or only limited ones.
One thing that the Photos app does not have is an internal feature to find duplicates. At the point of import it will flag whether the vid or photo is a duplicate, and one can then decide whether to import it or not. Once the duplicate is imported, however, there is no function that will allow one to find all the duplicates. Fortunately, there is an app that can be downloaded called PowerPhotos, that will let one search for duplicates in the Photos app library.
-- Rich
