Hi,
It is better to create MPN master records than to create as many materials as MPN due to following reasons:
1. For MPN material even if you do Goods receipt for MPN material the stock of internal material will get updated, if you maintain different materials then stock of that particular material only will get updated which may cause problem
2. you require less efforts to maintain MPN materials as there are only 3 views to be maintained for MPN (HERS) material type
hope this will help you
With regards,
Prathamesh