Freshly milled flour makes a sticky dough and products with less volume than those made with aged flour. There's actually a natural oxidation process for flour during which it turns whiter if allowed allowed to rest for several weeks after milling.
But, because time is money, in the US, chemicals are used to expedite the "bleaching," including potassium bromate and chlorine dioxide, to rapidly "age" flour, to make it whiter, and to give it better absorption qualities.
In Europe, most of those additives are banned. They let the flour sit in the air for a week or two, to bleach naturally, without chlorine, bromates and peroxides, since some of them are considered carcinogenic.
I haven't been brave enough to try unbleached flours on cakes...they won't be as soft and fluffy, I think. I have tried unbleached flours on bread and for that they've been fine.