Hello
After the activation of MRP areas in customizing, you must run the planning file entry conversion running report RMDBVM00 (or transaction OM0F). This is necessary because a new type of planning file entry is created.
If you don't change anything in master data or customizing, you won't see any difference, besides and extra field to input the MRP area on MD04 and another MRP transactions.
In order to start using MRP areas, you must first create them in customizing and after that assign them to the material master. Report RMMDDIBE02 can be used for mass processing.
BR
Caetano