Long ago, MPS (master production scheduling) was the input to the MRP
(material requirements planning) system. The MPS process was were end
item requirements were aligned with production plans and rough cut
capacity was done to check the feasibility of the schedule. In many
cases the MPS was also the assembly schedule. After everyone approved
of the plan it was feed to the MRP system for execution. Normally the
MPS would not create any plant or purchasing requirements, and MRP did.
This was also done because the early systems couldn't handle the
processing in one step. I remember coming to work on Monday mornings to
find that MRP was still running from the Friday night start. It also
allowed a break-point so that the master production schedule didn't
create production activity and purchasing activity that needed to be
changed which caused "nervousness" on the lower level components -
especially purchasing.