Question
Which files can be safely removed from C:ProgramDataPleskInstallercache to free disk space?
Answer
Deleting files from this directory is not recommended, since they are part of the installations that Plesk uses to update and, if something goes wrong during future updates, it would need some files of a release to repair it.
Additionally, if an update needs any of those files, it's going to need to re-download it again making the update process longer whilst there are files that are heavy-sized.
with the above being said, Inside the C:ProgramDataPleskInstallercache folder, the files that usually take more space are the ones in C:ProgramDataPleskInstallercachepoolrelease. So if it critical and the directory became too big, it is possible to delete or move files down to the current release version in C:ProgramDataPleskInstallercachepoolrelease to another disk.