Plan decomposition
Breaking work into tasks is where planning support genuinely helps, and it helps for a reason worth understanding.
Decomposition is a recall problem before it is a judgement problem. The failure mode in planning is rarely misjudging a task you thought of; it is omitting a task entirely. Testing, migration, documentation, training, the security review, the support period after launch, the decommissioning of the thing being replaced.
A model has seen a great deal of written project structure, so asked to decompose a familiar kind of work it produces a list that includes the categories your team routinely forgets. That is the value: recall, not judgement.
How to use it well. Draft the plan yourself first, then ask what is typically included in this kind of work that is missing here. That order matters, because starting from a generated plan anchors you to its structure, and the generated structure is generic. Starting from yours and testing it for omissions keeps your judgement and adds the recall.
What it will not do. Sequence correctly for your constraints, because it does not know who is available when. Size the tasks, per the estimation problem. Or know that your organisation requires a particular gate that no external corpus mentions.
And a caution. A generated plan is comprehensive, which is not the same as right. Comprehensiveness in a plan is a cost: every task listed is a task someone tracks. A plan that includes everything typical is frequently worse than a shorter one that reflects a real decision about scope.

