Hi,
"ERP: SPRO>Integration with other mySAP.com Components>EWM>Assign Warehouse Number to Warehouse Number of Decentralized SCM System."
This part is not technically necessary for deliveries or any communication actually. It is only be used in the CIF - but it is very recommendable, as it reduces the quantity of data transfered.
For details how this works, see this document:Material / Product master data in SAP EWM (Part 1)
Details are described somewhere in the middle, around picture 5.
The other mapping is absolutely necessary.
Brgds
Juergen