The short answer
No. Your data. Shrink it from its app; don’t delete the folder.
What is it?
The iMovie Library in your Movies folder holds your iMovie projects and events, the clips you imported (copied into it), and render files iMovie creates for smooth playback. It often grows to tens of GB.
Your iMovie projects and media. Render files inside can be deleted from iMovie and are recreated.
What happens if you delete it?
Deleting the library deletes your projects and imported clips. Only the render files are recreated, automatically, when you play or edit again.
How to remove it properly
To reclaim space safely, choose iMovie › Settings and click Delete next to Render Files. Delete events and clips you no longer need from within iMovie, or move the whole library to an external drive while iMovie is closed and open it from there.
From the app itself: iMovie > Settings: Delete render files.
Before you delete it
Export finished projects (File › Share › File) before removing a library: once it is gone, the edit cannot be rebuilt.
How MoreRoom helps
MoreRoom recognises this as your data and never suggests deleting it. It shows how much space it takes, so you can shrink it from its own app.
Frequently asked questions
Can I delete the iMovie Library on my Mac?
No. Your data. Shrink it from its app; don’t delete the folder. Deleting the library deletes your projects and imported clips. Only the render files are recreated, automatically, when you play or edit again.
Will iMovie libraries come back after I delete it?
No. Deleting the library deletes your projects and imported clips. Only the render files are recreated, automatically, when you play or edit again.
How do I remove iMovie libraries properly?
To reclaim space safely, choose iMovie › Settings and click Delete next to Render Files. Delete events and clips you no longer need from within iMovie, or move the whole library to an external drive while iMovie is closed and open it from there.