The “~/Movies/iMovie Events” folder is a large file size and takes up a lot of space on your hard drive.
You can store the files from that folder on to another hard drive.
- Make sure another hard drive is connected.
- Open iMovie.
- In the Event Library. Drag each event (marked with a purple square and white star) to the new hard drive.
Also, when importing, make sure to change the “Save to” dropdown box to the hard drive you want to use.