Many companies face the same contradiction: inventory is high, yet planners and buyers are busy chasing shortages every day. From the system side, MRP appears to be running, but the supply chain still spends too much time firefighting.
MRP and ATP are difficult because they are not only system functions. They require business understanding, planning discipline, master data, exception handling, and execution feedback.
Questions worth asking
Do teams really understand the difference between MTO and MTS? What is MRP actually calculating? Why does MRP fail in many companies, and are the difficulties solvable? What are the limits of MRP, and do those limits mean MRP should not be used?
When MRP seems to run but planners still adjust plans every day, what is the real cause? Which parts of the production planning system are practical, and which are only concepts floating in the air?
Where ATP fits
ATP, or material readiness checking, should answer a different question from MRP. MRP creates or recommends supply over time. ATP checks whether a specific demand can be confirmed based on available supply and planning rules.
The important part is how they work together: when to convert planned orders, how to expose shortages, how sales, planning, procurement, and production share the same supply picture, and what S/4HANA changes in the MRP layer actually bring.
So the useful discussion is not whether MRP or ATP is advanced. It is whether the company has built a planning system where these functions can play their roles.