This Advanced Boot Option is ideal in situations when you have performed some system changes and your whole computer freakes out. This utility will allow you to revert back to the previous configuration that is known to have worked fine.
System changes take place when installing new applications and drivers. New stuff may conflict with other software and cause the system to malfunction! Invoking the Last Known Good Configuration will restore registry settings and driver settings that were in effect the last time the computer worked fine!
Once, you logon with the Last Known Good Configuration, you cannot return to the previous configuration as the previous configuration has become your current one now!
Technically, the previous configuration settings in the registry are copied to the current location:
\HKEY_LOCAL_MACHINE\System\ControlSet001 –> \HKEY_LOCAL_MACHINE\System\CurrentControlSet