What are the advantages and disadvantages if using WM module?
 
Warehouse Management is always advantageous when the Inventory management could not handle the materials in storage locations. You can track the material exactly where it is stored and whether it is on the move or in storage bin.
 
Almost all the disadvantages from basic WM were the complicated scenarios that are handled thru Extended Warehouse management.
 
Advantages:
 
- Track exact stock location within one storage location with FIFO.

- Provides put away functionality for palletizing. etc 

- Provides better picking functionality .

- Allows for picking locations with replenishment when falls below a defined quantity.

- Allows segregation of stock types within a warehouse.
 
Disadvantages:
 
- Increased master data maintenance.

- Additional process step for receipt and picking.

- Requires expert knowledge to configure for maximum benefit.

- More complex to resolve problems caused by incorrect processing.
 
Generally WM provide better automation of processes, particularly with RF, but requires more maintain and process discipline. 
 
It is recommended that you used WM only if the standard logistics functionality is insufficient for your needs.

SAP WM Books
SAP Warehouse Management Certification, Interview Questions and Configuration Reference Books

Delivery Hints
SAP Logistics Execution

SAP Warehouse Management Tips
SAP WMS Discussion Forum and Warehouse Management Tips

Best regards,
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