Split BReps with planes sample

I have a question.

In the Split BReps with planes sample we used the PlaneSurface.CreateThroughBox(plane,bbox)
Why do we need the bounding box here? Is it because of certain tolerance issues?

A plane does not hold any information about a concrete size. Its basically a local coordinate system.
If you create a plane surface you’ll need that extra info. Basically an rectangle or size would be sufficient, but providing a (bounding) box allows a more general usage. For instance you can make it up to anothers object bounding box, and create a plane big enough to fully cut through .
You can also create a planar surface in xy space and orient (basis change) that to your plane. You’ll just need to make it big enough. Using the boundingbox of another object is just quite elegant.