Whole oat flakes are not cut before they are rolled, so they remain the bulkiest of the rolled oats. Oats are frequently used as a cooking ingredient, as in haggis and some varieties of sausage ...
For grains, that ends up erasing much of the apparent time-saving benefits. I'll still use my pressure cooker to cook whole, bran-on grains, because it doesn't do any harm at all, but I'll do it ...