This is a nasty way of doing things (unnecessary computation and memory overhead; poor interface design) ... but let's get it in as it stands and we can tidy it up if it proves to be a bottleneck.

However, I would like to see a comment here which describes the non-intuitive steps that are taking place:
```python
        # NB. This section is ripe for improvement:
        # - Internally self._points() expands coord.points to the same
        #   N-dimensional shape as the cube's data, but it doesn't
        #   collapse it again before returning so we have to do that
        #   here.
        # - By expanding to N dimensions self._points() is doing
        #   unnecessary work.
```