Yes, free protection - mostly on granite, in pairs for opposition on narrower flakes or at large flake tops. I do also use them a lot in opposition with other types of pieces as well.
ala: Ken Nichols, that boy has some scary but effective opposed hook techniques. Consult his Rock and Ice artical circa 1987 (I believe) for similar stuff.
Cool stuff JH, perhaps a small dissertation on your techniques would be in order, unique and insightful into a realm that is often overlooked or ignored.