Buds are actually nothing more than tiny, modified leaves with flowers growing between them. That said, cannabinoids can form on virtually any surface of the plant. Some strains are so potent that the buds run out of places for more keif to form, so it starts forming on the surfaces of the leaves. You know a bush is the real good shit when the leaves are frosted over. These are the kind of leaves you can smoke. If your leaves ain't covered in keif though, don't bother!
I usually use the leaves as a substitute for blunt wraps. The practice is actually quite common apparently, and the finished product is known as a magar