Redwood - Supply planning, Buyer planning, IO planning

In Fusion Supply Planning, Safety Stock / Inventory Optimization-related capabilities are available within the Supply Plan options. However, I notice that Oracle now also provides Inventory Optimization (IO) as a separate plan type. In addition, there is Buyer Planning, alongside the standard Supply Plan.

Please help clarify the rationale behind this architecture. I would like to understand:

• Why is Inventory Optimization available as a separate plan, while safety stock planning capabilities continue to exist within a Supply Plan?
• What additional capabilities or business use cases does the dedicated Inventory Optimization Plan provide compared with calculating safety stock directly within a Supply Plan?