Are you wanting to put a set of data into multiple tables - without needing a primary key from the first table? I ran into a situation where I had records that I wanted to insert into a table, but I wanted to be able to email people saying "hey look you need to do this, this and this because there are new records to look at!". So, I wanted to use the same exact set of data and put it in 2 tables (1 as the actual source, the other to use as a mail queue).
Voila - Multicast! It allows you to use the same recordset in multiple destinations. Wonderful!
Hopefully this helps someone else who runs into this issue.