Whilst it's true that you don't get stuck sparges with BIAB, a good crush with the "right" husks can cut down on flour. Remember that even though BIAB can handle flour, the flour doesn't magically disappear during mashing - it ends up as the murky protein and general crap in the vessel after lifting the bag. So I assume that even with BIAB you would still get less murk with a more even crush. Also slow lifting does form a grain bed in the bag, so I'd guess that grain bed would form a better filter with a better mill.