Procurement type does not affect MRP processing key,
During regenerative planning, all materials are planned for a plant. This makes sense when you are carrying out the planning run for the first time as well as later during production if data consistency cannot be guaranteed due to technical error.
The disadvantage of regenerative planning is the fact that the system has to deal with high capacity loads because all materials are planned, including materials, which may not be affected by the planning run.
To overcome this disadvantage, it makes sense during production to carry out the planning run using the net change planning procedure. The only materials that are included in the planning run are those, which have undergone a change relevant to MRP since the last planning run, for example, because of warehouse issues or sales orders, changes to the BOM and so on.
The net change planning procedure makes it possible for you to execute the planning run in short intervals, for example, in daily intervals. You can thus always work with the most up-to-date planning result.
You can use net change planning in the planning horizon to shorten the MRP planning run even further. The system then only plans materials that have undergone a change relevant to MRP within the planning horizon. In order to also plan changes outside of the planning horizon, you must execute the net change planning run in greater time intervals.
You define the planning horizon per plant or per MRP group in Customizing for MRP in the IMG activity Define planning horizon. The planning horizon should be at least long enough to cover the period when sales orders are received. It must also accommodate delivery periods and the total lead times of the materials.
With NETCH: All materials will be planned which have undergone for a change relevent for MRP since the last planning run like change in stock, material master or creation of new receipt etc.
With NETPL: All requirements will be planned which falls under the planning horizon from the day of the MRP run irrespective of changes were done or not. Planning horizon will be define at plant level in OPPQ transaction.
NETUL: Irrespective of changes all materials will be planned within a plant..with these key planning file entries will be created for all materials which are relevent for MRP for example MRP type PD. This type of plannig recommends at the time of implementation (first MRP run for new plant) or if the system is down since long time so the planning entries are not created.
This has no impact with procurement type. Procurement type has integeration with planning control parameters like create planned order or purchase requisations.
As a example,
Your planning Horizon maintained in Configuration is 120 Days for a plant.
Your demand for the coming 6 months in the demand management is,
Jul : 50 Kg
Aug:100 Kg
Sep:10 Kg
Oct:25Kg
Nov:30 Kg
Dec:10 Kg.
If you are running MRP with the NETCH key system will consider all the demand available in the system & create procurement proposals. If you are running MRP With NETPL key system will consider only the Demand laying in the Planning horizon ( 120 days from the current date). i.e it will create procurement proposals only for the demand till Oct month.