If no schema is specified, run-time schema discovery is done. - This is HUGE, no longer do you need to create multiple send flat file schemas. You simply need to create one with a flat file assembler that does not have a document defined and then across your entire BizTalk enviornement, you can reuse this. BizTalk is now smart enough to create the flat file according to the schema that defines it and it saves the re applying of bindings when changes are made to the flat file schema.
BTW: Be aware that this functionality only exists in the Assember. This feature is NOT available in the disassembler. When a flat file is recieved into BizTalk, BTS (BizTalk Server) needs to know which schema to validate against. If you do, you will get a build error stating that there is no schema specified.