When using the iCloud Windows Sync Client you have the option to also download 'high-efficiency' files. This means that the iCloud Client will not only download files in JPG and MOV format but will also additionally download these files in HEIF format. HEIF is great because it compresses better, but it is not as platform-compatible as JPG.
Unfortunately, there is no option in the iCloud Client to only download files in HEIF format.
This scrpt checks if the same file is available in HEIF format and will subsequentely delete the corresponding JPG or MOV file.
Please use the Windws 7/8 version of the iCloud Windows Tool. The newer Version do not allow you to download your complete photo library.