The correctness, accuracy, completeness, and usefulness of a Schedule Quantitative Risk Analysis (SQRA) depends heavily on the quality of planning data used for input or, plainly, the quality of the project schedule.
A good quality schedule brings about good, and reliable quantitative results. Good quality begets good project management that begets good results.
The consequences of a poor-quality schedule are practically endless. If unaddressed, the schedule remains counter-intuitive, disconnected, or disjointed, resulting in poor project control.