Often, SketchUp models can be a great foundation for sketching, where the model serves simply as a guide for the sketch. In that scenario, it’s not uncommon for the SketchUp export itself to be removed altogether from the final perspective. Still, the shadows from the SketchUp model can be useful to quickly apply shadows to even the hand-sketched scene.
This video walks through a process for exporting only shadows from SketchUp models so that they can be applied to hand-drawn perspectives.