Parametric estimating isn't Parametric estimating often assumes projects are very similar. But each project is unique. When projects step outside the usual, this method might not work well. Parametric estimating doesn't always bend to fit new situations, which can lead to mistakes in planning.for the start of a project. It's a tool you can use at many points. Early on, it helps give a clear picture of what resources you need. Later, if things change, you can adjust your plans using the same reliable method