There are two main reasons to move your iMovie files to an external storage drive. One is that video files take up a LOT of space, and the non-destructive editing that iMovie does can also add to the file load on your main hard drive (or SSD, in the case of a MacBook Air). The other is organizational – you might want to put all your stuff in one, easily accessed place for later retrieval and further editing.
Lucky for you, then, iMovie makes this pretty easy. Here’s how.