Microsoft Knowledge Base Article 324347 contains the following summary:
This article describes how to use Powercfg.exe, a utility that was introduced in Windows Server 2003 family. You can use this tool to access the settings from the Power Options tool in Control Panel and to set these settings from a command line (if you are an administrator). Powercfg.exe has additional functionality to extend some settings that are not available in Control Panel. You cannot use this tool to configure all of the settings in the Power Options tool; you can only configure the settings that are described in this article.