A planning tool gives you a number. Talented people give you their best call. Neither one shows you where you'll come up short.
The work starts the same way every time: a model of your real demand patterns, the way your network interacts tier to tier, and the rules your planners actually follow. Run it across hundreds of scenarios and it returns a tested performance profile, not a single optimal number, on your own data. You see your current policy beside an optimized one, total inventory down with service held or improved, and the model still holding when a disruption hits: a demand spike, a supplier delay.
Who builds it and who runs it depends on where you're starting from. Either way you keep a decision model your planners use as part of normal planning, not a report that sits on a shelf.