When you make changes to the Windows Registry manually or when changes are made to the Windows Registry during the installation or uninstallation of a software or device driver, Windows 8 or Windows Server 2012 does not make changes to the registry right away.
Such updates to the registry are not flushed right away to the disk. Instead of this, what the new operating system does is that the modified registry data is flushed to the disk regularly in short intervals of time.
Now, after changes are made to the registry, if you are faced with a scenario where the computer shuts down immediately, due to power failure or any such unexpected reason, the registry changes may not get saved. In this case, you may find that, when you start your PC back, the application may not work correctly and the registry changes may not be visible at all. In fact even newly installed driver may appear NOT to have been installed – or the uninstalled drivers may continue to appear as being installed.
In such situations, you should make the registry changes, install or uninstall the software or driver once again.
All pending disk write requests, including such registry changes are saved to disk before the machine is powered down, that is, during Shutdown, Restart, Hibernate and Sleep options.
Do note that if you have set the power button to Do Nothing, via Power Options, the pending disk writes will not be saved.
If you wish, you can make Windows 8 write the registry modifications immediately to disk. For this you will need to use the RegFlush API. However this operation is expensive in terms of resources used and may affect your systems performance.
KB2784761 say that this is therefore done this way, to maximize the performance in Windows 8.