What does userinit.exe do?

According to the documentation for the Userinit registry key on TechNet, userinit.exe does the following:

• Runs the logon script
• Reestablishes network connections
• Starts the configured Windows shell (the default is Explorer.exe)

I realize this was answered, but here is the details of what userinit.exe does (Explorer.exe is technically loaded by winlogon.exe)

Userinit applies Group Policy settings and any applications not trumped by said group policy that are stored in the Registry locations for startup programs, this is a very long list that is ever-evolving and is accessible via a google search or off from Microsofts website.