Mac storage basics · Creative and media apps
Does trimming a video in Photos save space?
Short answer: No — Photos keeps the full original so the trim can be undone. Export the trimmed clip and delete the original, or trim in QuickTime Player and save the shorter file.
Not by itself. Photos edits are non-destructive: the trimmed version plays, but the full original is kept so you can undo the trim later. The library can even grow, because the edited version is stored too.
To genuinely save space, export the trimmed clip (File → Export), import the shorter file, and delete the original from Photos (then from Recently Deleted). Or trim in QuickTime Player with Edit → Trim, which saves a new, shorter file you can keep instead of the original.