Example1: Lets say we have sales data.
category columns might be Year, Month and day
none categorie columns might be Customer, Sales rep, amount, productgroup.
Now there might be use to sort within the day (a categorie) in some cases by Sales Rep, in other cases by Customer and again in other cases by productgroup. Currentyl this means in this example 3 Views. (In real life databases, with a few parameters more, often enough 50 or 100 with only a few columns more).
The current way of resorting by a column (lets say the sales rep) to remove the categories, is not only casing the problem, that often the data of several years are not wished, but also, that the disappering categories mean that usful information is disappearign on the view level (in what year and month was this dataset?)
Example2: Lets say we have a single category empedded view (maybe Sales related documents, to keap in the same area) in the adress form of the customer.
Now it would be nice to resort within this customer (just like above)