Work with multiple libraries
You aren’t restricted to storing all of your photos in one library – by which we mean the library file you see in Finder; you can have only one iCloud Photo Library. So, you could use one library for family snaps and another for competition entries.
You can make use of this as a remedy if your whole collection is too large to fit in your iCloud storage, though it means making some hard decisions about what gets uploaded and, consequently, is available in an instant on all of your devices. Only one library file on your Mac can be designated as your System Photo Library, which is the only one that will sync with iCloud. Others simply won’t do it. You can’t work with a single library on your Mac and tell Photos to exclude certain things from it going to iCloud, as you might tell Time Capsule to exclude folders or drives from its backups.
To create a new library, hold å while opening Photos. The dialog that then appears lists known libraries on your Mac, and contains a button to create a new library. Once you have multiple libraries, you can switch between them just by double-clicking one in Finder. the latter option, editing a photo downloads the original so you can work with the best version available.
It’s a smart idea to have at least one Mac set to receive photos at their full quality, and to maintain an offline backup of that library in case anything bad happens to your iCloud account. If space on your Mac’s startup disk is limited, you can move your System Photo Library to a larger, external drive to accommodate this.
It’s smart to keep an offline backup in case problems occur in iCloud
Photos’ alternative startup method reminds you which are the System Photo Library and the last opened library.