photos is still using 128 GB storage even with everything in iCloud
I have asked to optimize storage with everything in the iCloud but it is showing Photos using 128GB storage on Mac HD
iMac Line (2012 and Later)
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Even with the optimize option, there will still be data stored on your Mac. Thumbnails and low-resolution copies of the photos and videos are kept in the local library as is all of the metadata (keywords, date and time, geolocation info) for the items in your library.
Additionally, Photos is notorious for not properly reporting the actual amount of space used on disk in the photo library. There are some things you might be able to do to get that reporting fixed temporarily but it will just happen again. I'm at the point where it just doesn't matter to me anymore. The disk itself knows how much space is used but the .photoslibrary package in Finder will misreport it at times.