A: There are many types of OS updates or applications that need to replace files that are currently in use or involve configuration that only takes effect when the computer starts. To enable files that are in use to be replaced, the OS or software can place a request with the OS that on next startup, files are switched before they are loaded as part of the startup process. Updates ask you to reboot so these changes can take effect. However, manually shutting down then starting at a later date has exactly the same effect, and pending file replacements or changes will still occur.