Important settings
Understand exactly what each of Photos’ preferences does
Explore Photos’ preferences and you’ll discover a bunch of useful options, listed under General. With ‘Summarise photos’ switched on, collections and years show thumbnails for just some of their contents. Turn it off and you can scrub along them to see thumbnails of everything in them.
There’s also an option here to strip out location info when you publish photos, helping to preserve some privacy. The ‘Reduce motion’ item is intended to make Live Photos easier to view, though you can use it to speed up navigation, as it gets rid of many of the app’s fussy animations. The current library’s location is shown here, too. Even with one library containing all of your photos, you may want to move it off your startup disk to give yourself plenty of free space there and the library more room to grow.
Unexpected iCloud settings
Despite the iCloud preferences tab, a couple of items under General have a profound effect on iCloud Photo Library. The button that sets the open library as the System Photo Library revokes that special status from the existing one. Photos already in iCloud then download to the newly designated one, and its contents upload.
Also, the option to copy imported items into Photos’ library is of critical importance. You may be tempted to turn it off if you use a standalone camera and like to organise snaps taken with it in a folder hierarchy you’ve devised, independently of whatever albums you create in Photos, and have the app’s local library merely reference their external location. Sadly, this scenario is incompatible with iCloud Photo Library; Photos will only upload items to iCloud if they’re stored in its monolithic library file, which is where they are placed if this setting is on.
Copying photos into the library is vital if you want to sync them with iCloud