How to manage the space Photos takes up on macOS?

I have photos synced through iCloud to my Mac. This is good. I like to be able to see the pictures big! However I don't have a lot of storage space and the library seems to grow and grow, even though I have checked "Optimize Mac Storage", but it doesn't seem to do anything. I recently got the message "There is not enough disk space to open your library." when trying to open the “Photos” app. Is there a trick to get it to *actually* optimize storage? Or a way to prune some files that are currently saved to disk? I've seen a lot of other questions where people don't want their photos library on their Mac.. I would like to use the Photos application as I really like it other than this issue. I just want to also be able to have a computer with enough free space to operate.