User exits in SAP are points where you can add custom functionality to standard SAP programs without modifying the original code. They are particularly useful in modules like Sales and Distribution (SD), Materials Management (MM), and Production Planning (PP). Here are some real-world examples for each module:

1. Sales and Distribution (SD)

• User Exit for Pricing: In the pricing process, you might need to implement custom logic to apply specific discounts based on customer groups or order types. You can use user exit USEREXIT_PRICING_PREPARE_TKOMK to modify pricing conditions before they are calculated.
• User Exit for Sales Order Processing: The user exit USEREXIT_SAVE_DOCUMENT can be used to implement checks or validations before a sales order is saved. For instance, you could prevent the saving of orders if the total value exceeds a certain threshold.

2. Materials Management (MM)

• User Exit for Purchase Order: You can use user exit EXIT_SAPMM06E_007 to add additional checks for purchase orders. For example, you might want to validate vendor credit limits before allowing the creation of new purchase orders.
• User Exit for Goods Movement: The user exit USEREXIT_MATERIAL_UPDATE allows you to implement custom logic during goods movements, such as automatically updating stock information in a custom table when goods are received.

3. Production Planning (PP)

• User Exit for Production Order: User exit EXIT_SAPLOEVA_002 can be used to add custom checks when creating or changing production orders. For example, you might want to enforce specific routing checks based on production lines or materials.
• User Exit for Material Requirements Planning (MRP): In the MRP process, you can use the user exit EXIT_SAPM02D_001 to implement additional calculations for planned orders, such as adjusting lead times based on historical data or supplier performance.

Implementation Tips

• Use Transaction Codes: You can find user exits using transaction codes such as SE84 (Repository Information System) or SE37 (Function Module).
• Debugging: Utilize the debugger to understand the flow and how your custom logic will interact with standard SAP processes.
• Documentation: Always document any changes made through user exits for future reference and to assist in maintenance and upgrades.

These user exits provide flexibility and help meet specific business requirements while maintaining the integrity of the standard SAP system.