Mac storage basics · External storage and adding space
Does dragging files to an external drive move them or copy them?
Short answer: Between different drives Finder copies, so the originals stay and no space is freed. Hold Command while dragging to move, or delete originals after checking the copy.
Dragging between different drives in Finder copies — the originals stay on your Mac, so no space is freed. Hold Command while dragging to move instead (the pointer changes), or delete the originals after checking the copy.
Dragging within the same drive moves. For big or important folders, copy first, check the copy opens, then delete the original — or use a tool that verifies the move and leaves a link behind, such as Storage Studio.