Having worked in the software industry for decades as a Tech Support / QA Manager... well maybe a bit longer. I can honestly say that programmers rarely if ever bother to clean up after uninstalling a product. Files and directories that are in use may remain after the uninstall process has completed. Registry entries are even far worse. Especially those that try to prevent you from continually installing trial software. Another mean trick is writing to areas of the hard drive that are supposed to be reserved for the file system. This means even if you reinstall Windows they may be able to block reinstalling a trial version. Yes, I know this all first hand.
So, editing the registry is an old trick to remove some components that may be causing problems. However in the case of Armory Crate and Aura Create, it is unlikely to matter since there is no way short of restoring Windows to a previous backup will fix the problem with AC/AC. The software tries to update all on it's own and eventually you have to restore again.
So if you know what you are doing, removing registry entries from Windows you can solve some problems. But none likely that are related to AC because you can only install the current version. ASUS has no means that I could find for installing an older version.
About two updates ago they broke my CoolerMaster fans lighting. I guess I am going to have to go through the pain in the butt of contacting their support only to have them run me through all the stuff I know won't help or work. This software has been some of the buggiest I have seen and I was a huge ASUS fanboy prior to this. My boss had to get on to me for having too many ASUS systems in our lab. I loathed MSI and Gigabit systems. Intel was okay mainly because they were so cheap.