Most people would say if your doing a paint correction; you shouldnt "need" a glaze. That being said, if your working by hand (I think most people would use Wolgang Polish Enhancer by hand as a "paint cleaner", but it could be used by machine) glazes can help "amp up" your finish or temporarily hide minor imperfections. If you have the time, budget, and desire - no reason not to use a glaze, especially if working by hand. But again, keep in mind, glazes are like make-up; they are a temporary fix.
IMHO, if your into detailing and own a black car, you really need to learn how to work by machine for polishing / correction. I cant imagine spending hours "detailing" a black car, only to look at shiny swirls when your done.