The primary purpose of iCloud is to keep the documents and data on all your devices identical and in perfect sync, while all documents and data are stored safely in iCloud. The content of iCloud will be mirrored on all devices with local shadow copies. So, you will not necessarily save storage on your devices.
The only way to save storage on your Mac is to use iCloud Drive in combination with "Optimise Mac Storage". There is a checkmark in the System Preferences > AppleID > iCloud, at the bottom of the panel. There is another "Optimise Storage" option in the preferences for Photos, Photos > Preferences > iCloud".
With "Optimise Mac Storage" enabled, iCloud will remove local copies of items that you have not used in a long time, when the storage gets low.
See: Set up iCloud Drive - Apple Support
and: Turn on Desktop and Documents
Also enable iCloud Drive and the option "Desktop&Documents" to move the content of the Desktop folder and the Documents folder to iCloud Drive.
To save storage for your photos, see: Learn more about iCloud Photos