In some business scenarios you may be required to receive a batch file that must be broken up and processed as single messages by BizTalk Server 2004. This could allow for individual record level processing, selective content based routing, or single message mapping.
Get more information from the original blog post on this topic: http://www.biztalkgurus.com/blogs/biztalk/archive/2004/12/13/Debatching-Options-and-Performance-in-BizTalk-Server-2004.aspx