In ways both more free, and more restrictive than regular sorcery, Elemental Affinity is a type of sorcery which does not rely on racked spells, spells and effects can be cast on the fly. On the other hand, the magics are strictly based and must derive from those elements.
By taking this sorcerous path, there is an affinity or attunement, being 'aligned' with that elemental power such you have conscious (and a certain amount of sub-conscious, the way things 'react' to your moods at times) control over that element.
Attunements based on more than two elements is not possible under normal circumstances. Since the Attunist is very much connected to the elements, having more than two attunements sets up a conflict within the sorceress, and unless special circumstances permit (eg. a dip in the Fount at the Keep of Four Worlds) such an attunement is not possible.
Thanks go to Arref Mak and
Mike Levay