Maybe just reads "a bit odd".  The "can also be used for \<aggregated-by>" hasn't really been 'previously mentioned'.
How about (something more like ?) ...
""" For instance, \<Collapsing entire data dimensions> discusses how to use \<MEAN> to _collapse one dimension of_ a \<Cube>, and also _how to_ perform weighted \<Area averaging>, _while_ \<Partially reducing data dimensions> shows how to regroup data to get fewer points in a dimension. """