When looking at data in a hierarchical cross table with multiple headers and sub-totals it is sometimes useful take the hierarchy into account when doing the sort. E.g. For a grouped table that show the sales of different products by customer one might want to first sort the table by customer sales and then by product sales within each customer.
Currently the cross table only allow you to chose between sorting the rows within each group (while leaving the groups themselves sorted alphabetically) or ignoring the hierarchy altogether.