SharePoint protocol support was integrated into Microsoft Office in version 2007, and is the standard way of integrating Alfresco and MS Office.
The plugin provides support for:
Checkout / checkin
This plugin is useful for earlier versions of Office (2003 and XP) and use cases that are not well supported by the SharePoint protocol. The plugin does not currently integrate with the Alfresco Share interface, but instead uses the older Alfresco Explorer interface.