NOT as to what you do within CTM; but here's my 2 cents for the Detail Scheduling:
CTM is great at generating feasible plan based on order base prioritization. However PPDS support a much more variety of "Detail Scheduling Capability" i.e. Sequencing of your planned PPDS order. E.g. CDP (Characteristics Dependent Planning), Block Planning, Production Campaign & Setup Optimization are all available within PPDS only. Of course, this added capability comes with its own additional master data requirement and trade-off.