In SAP Materials Requirements Planning (MRP), what is the main purpose of specifying a planning horizon when you use a net change in planning horizon (NETPL) MRP run?

Introduction / Context:
In SAP MRP, different planning types and horizons can be used to balance planning accuracy with system performance. The planning horizon is a time period in which planning relevant changes are considered when using a net change in planning horizon (NETPL) run. Understanding how the planning horizon interacts with NETPL is important for optimizing MRP performance and is a common topic in SAP PP and MM certifications.

Given Data / Assumptions:

• The MRP type in use supports net change in planning horizon (NETPL).
• A planning horizon is defined in customizing or in the material master.
• The question asks for the main purpose of specifying this planning horizon.
• We assume the reader understands the difference between NETCH and NETPL planning types.

Concept / Approach:
NETPL (net change in planning horizon) is an MRP procedure that includes only materials for which there have been planning relevant changes within the defined planning horizon. The planning horizon limits how far into the future the system looks when deciding whether a material needs to be planned in a given run. By restricting the run to a defined horizon, system load is reduced while still ensuring that imminent requirements and changes are considered. The planning horizon does not directly decide whether forecasts are considered, does not filter by procurement type and does not itself choose between NETCH and NETPL; rather, it is used within NETPL to decide which materials are included.

Step-by-Step Solution:
Step 1: Recall that in NETPL, the system considers only materials with planning relevant changes in a certain future time window.Step 2: Understand that the planning horizon defines this time window, measured from the planning date into the future.Step 3: Examine option A, which states that only materials with planning relevant changes inside the planning horizon are included in the MRP run when NETPL is used. This is exactly how NETPL and planning horizon interact.Step 4: Examine option B, which mentions forecast inclusion. Forecast inclusion is controlled by other settings, not by the planning horizon itself.Step 5: Examine option C, which restricts NETPL to externally procured items, which is not the function of the planning horizon.Step 6: Examine option D, which describes choosing between NETCH and NETPL. This choice is made when configuring MRP types or running MRP, not by the planning horizon.Step 7: Conclude that option A is the correct description of the purpose of specifying a planning horizon for NETPL.

Verification / Alternative check:
SAP help for MRP procedures explains that NETPL looks only at materials that have undergone planning relevant changes within the planning horizon. Changes outside of that horizon are not considered in the current run, which improves performance but still ensures near term requirements are met. The planning horizon can be maintained in the MRP settings, and NETCH runs ignore it, considering the entire horizon instead. This confirms that the main purpose of the planning horizon is as stated in option A.

Why Other Options Are Wrong:
Option B confuses planning horizon with forecast control; forecast data usage is governed by other parameters such as consumption modes or forecast requirements types. Option C suggests that the planning horizon has an effect on procurement type filtering, which is incorrect; procurement type is defined at the material level and is independent of horizon. Option D treats the planning horizon as a switch between NETCH and NETPL, but the choice of planning type is made separately from horizon definition.

Common Pitfalls:
One pitfall is to think that planning horizon limits how far MRP plans requirements in general; in reality, it specifically affects which materials are included in a NETPL run based on changes in that period. Another is to overlook the difference between NETCH and NETPL and assume that defining a planning horizon will have the same effect for all planning types. For exams, remember that the planning horizon is particularly relevant for NETPL and is used to filter materials based on recent changes within a specified time window.

Final Answer:
The purpose of specifying a planning horizon is to ensure that only materials with planning relevant changes inside the planning horizon are included in the MRP run when NETPL is used.