When a mesh is created the vertexData for the mesh is maintained unless updated by the user. The position, rotation, scale of the mesh is stored in its worldMatrix which is then used to render the mesh in the correct placement and orientation. The worldMatrix is calculated, normally, just before rendering takes place.
When you write code that alters the position, rotation or scale of a mesh there will be times, as per your example, when there will be need for the worldMatrix to be known to change the state of the mesh. Since no rendering takes place when you write the code to implement the change of state in these cases the worldMatrix needs to be computed first.
Also if you search the forum for computeWorldMatrix you will find the examples where this is offered as a solution to give you more understanding.