This info is especially useful to system administrators, but other power users should find this useful. Periodically Microsoft releases Hot Fixes to patch bugs in Windows and other products, this key contains information about which Hot fixes have been installed.
You can also see this information when using “Add/Remove Programs”, and ticking the “Show Updates” checkbox. Start/Run/Regedit
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\ CurrentVersion\Hotfix