I interpret cableman's RRV to be more a recognition when the amp and speaker click and they react with the room optimally. What I mean is an amp and speaker when matched well should result in the cones moving at optimum excursion with the amp exerting at optimal output. A well balanced pair. On top of that, those 2 need to work synergistically with the room. If all that is balanced well, there would be a small window of volume adjustment necessary when playing most all music where your preference of optimal performance is achieved.
Please note I say "your preference". I do believe a good system in a good room would have a somewhat wide window for volume playback where the system is still in its sweet spot. As others noted, your "mood" may dictate volume. Maybe its Friday, you have Bruno Mars going and its pumping loud. Maybe your winding down from a hard day and its Vivaldi only moderate. Either way, in a certain volume range the overall system would still be in its stride.
I do remember a couple years back listening at Jazdocs home. I don't remember him ever touching the volume as we went through album after album. His volume was never loud. It was alive and enjoyable. There was definitely a sweet spot in his listening space. And the mood of the session said leave it alone.