Hi Umesh,
Note that in the rules of engagement, there is a requirement that says that you should perform searches before post a question.
There are lot of thread and different forums in which you can read about it.
Here you have a few:
Understanding MRP in APO and SAP ERP - SAP Planning
General Discussion - Why to choose APO over R/3 for planning?
One comment: in all the FMCG in which I worked, Finished and Semifinished goods are planned in APO thru Heuristics and Optimizers, and Raw Materials are planned in ECC.
Kind Regards,
Mariano