VW gets you to consistent power if the resistance of the atty/carto changes over time, as well as if you change cartos/atties, say to use a different eliquid.
Only for me it is a shrug. I use good cartos/atties, and have a real all-day-vape so run the same setup all day, every day, other than for a carto change every 20 ml or so. I get little noticeable resistance shift in the atties/cartos, would just nudge the wheel a little if I wanted a change. I may nudge the voltage up or down slightly at other times, but it is really rare, and frankly would be doing the same with VW, since those occasions are ones where I've wanted to change the net power a little.
The aspect of the power output being saved if you switch to a completely different carto/atty is also a shrug to me. I don't flip tank/carto during the day, to run different flavors, and even if I did I have been vaping long enough to know that different flavors are better at different voltages/powers. I like my vanilla tobacco at 8 - 10W, the preferred voltage/power will vary a bit but that's the zone. My vananaberry I run cooler, some straight up tobacco flavors I would run hotter. Adjusting a wheel up, whether for higher voltage or wattage, or down to decrease, is something I would be doing whether VV or VW if I was completely changing resistance or flavors.
I do care about consistency, that once I set the voltage (or power) for a given resistance, the device stays there, and at that the notcigs electronics are excellent. Loaded voltage will read slightly lower than unloaded, however what I've seen is real consistency in the output once it is set at a given point. A fresh set of batteries with a carto shows say 4.9V under load, measured with my separate meter, and I'll get the same 4.9V just before the batteries need to be changed.
So, net, for me, at a practical level the two do the same thing. Then again I'm also a person who doesn't care about digital voltage or ohms readouts -- I don't mind them, just that they don't matter, I set power to taste not to a meter.