Apple's iCloud is handy in that it lets you have access to your files on multiple devices that have internet access. But what's actually stored in iCloud isn't that obvious to the user.
This seems to be the case for Macworld reader Izabella. She asks why iCloud isn’t reducing storage on her MacBook more than it is. She sees iCloud storage on her computer taking up 80GB of storage but says she’s paying for 200GB of iCloud storage. “I want to use this space for other things,” she notes.
iCloud doesn’t necessarily save you storage, as confusing as that is, because it’s a mix of synchronization and cloud-based storage options.
iCloud Photo Library syncs all your photos and videos, but unless you set Photos (in Photos > Preferences > iCloud to Optimize Mac Storage), the full-resolution file for each piece of media remains on your Mac. Check that box, and you could save 80 to 90 percent of a library’s size.