Photos currently take up about the bulk of my used storage. Of those, I've noticed about half of the used space comes from a folder called "Masters", while the other half comes from the above folder. So, what is its purpose? Can I delete it to save space?
Check the file dates. If they are all old, this might be a temporary cache that did not get cleared.
Note that we have no inside knowledge of the Library file.
And on my Mac, there is a temporary folder, but it does only contain one empty subfolder. It seems to be a temporary cache, that will be automatically emptied, when the image files inside are no longer needed.
I am using Photos 4.0 on macOS 10.14 Mojave. Which Photos version are you using?
Not sure, but when I examined the contents of my Photos library, there is no "temporary" folder where you indicated. There is one called "derivatives" which from earlier posts is where Photos stores its generated thumbnails.
What is "~/Pictures/Photos Library.photoslibrary/resources/proxies/temporary"?
