I saw the clipping box mentioned in a few wishlists.
Another useful thing would be Clipping Box Reversed, where the geometry inside the box is not visible while the things outside are. This will work well when studying voids in various positions and sizes, such as shafts inside a building. (Of course, for a final solution BooleanDifference or MakeHole would do)
It would be useful to be able to transform any extruded geometry into a Clipping Box or a Clipping Box Reversed.