I personally think that SetDefaultFilePermissions: should only be used on files or folders that will remain on the OPs system. The reason is that the owner will be set but usually leaves all permissions blank. The OP can then set permissions as desired or if the OP isn't experienced you can set them through a script but this can be more work than it's worth.
Unlock: sets the owner as well as giving permissions to Everyone. So it leaves the file or folder wide open as far as permissions go. But if the intent is to remove these files then it makes perfect sense. This one also can work on registry keys.
So it gives you a choice.