Correct, a cold or dull fire will usually die or give you some grief minimum if shaken in that state. The coals should have a vigourus glow (hot) before shaking, by opening the ash door you can get a huge draft going to wake up what is left. Shaking then knocks down the ash and the fire can be banked. If the fire is not hot the ash will just will just lay there and snuff whatever you've got left. A fire that is already roaring would not need this process, but after a 12 hour burn your fire is beyond it's peak and on it's way out, it may need a little freshener to wake it up before loading. If you are well beyond that and losing the fire you may be able to save it by the same process. It will take a longer time to ramp up and you may have to load just a little at a time like a new fire, but you can usually recover it if there is a little life left in it. I have a stack thermometer and generally like to see 50-75 degrees rise before I shake. That should take a minute or two at the most for a healthy fire, if it takes much longer the fire is not happy. You can pretty much do anything to a roaring coal fire and not hurt it, but the units we use to heat homes really never ask Anthracite for that. Generally speaking these units are at the bottom of the scale and run the stuff fairly low temps compared to what it can really do which is the problem. Anthracite wants to burn hot, the colder it is the less it likes to be played with. Don't forget, it takes about 900F just to light it, so it is happier at 2000-2200F than it is at 900-1500F where we run them.