The difference between a quick quench and a slow cool is the size and pattern of the micro-grain structure. A very slow, long duration cool (equivalent to leaving in a furnace and lowering temperature over a long period of time) results in minimal grain formation, and very large grains. A quick cool will result in very small grain structure. Both have their uses in different metallurgical applications. Neither one is better than the other although one process may be more suited to the application that it is being applied to. I anneal my bullet casings so that I may reload them many times without the work hardening splitting the bottle necks, I only heat the necks of the case and once they are at the proper temperature, I push them over in to a water bath. Hope this helps.