Change where Photos stores your files
When you import photos and videos into Photos, they’re copied to and stored in the Photos library. If you prefer, you can store photos and videos outside the Photos library (for example, in a folder on your Mac or on an external drive) and still view them in Photos. Files stored outside your library are called referenced files. For more information about referenced files, see Where are my photos?
Referenced files aren’t automatically uploaded and stored in iCloud Photo Library, and they aren’t backed up along with the rest of your files when you back up your photo library—you must back them up manually. If you want to avoid manually backing up referenced files, you can move or consolidate the files into your library.
Store imported files outside the Photos library
Choose Photos > Preferences, then click General.
Deselect the “Copy items to the Photos library” checkbox.
Now, when you import photos or video, Photos leaves the files in their original location and accesses them as referenced files.
Copy referenced files into a Photos library
You can copy referenced files into your photo library so they’re easier to back up and are automatically included in your iCloud Photo Library.
Select the files that you want to move into the photo library.
Choose File > Consolidate.