Physical Points

A point is an idealization. On the scale of a building, the end of a spike is small enough to be considered an exact location, a point. But on the scale of your desktop, its end does not exactly define one location. For the scale of a desktop, the spike would have to taper to a pin point. Then, perhaps, you could consider its end to define a point.

But if you put that pin point under a microscope, then for that scale it is again too blunt. It would have to taper further, perhaps to the thickness of a bacterium, before the end could define a point. But now, on the scale of bacteria, the end of the spike is again too thick to exactly define a location.

So, points in 3D space are an idealization. For a computer model of a building, the sharp end of a spike is exact enough to be a point. The edges, planes, and other shapes that make up the building do not need to be specified to any greater accuracy.