Regarding the "difference" between variable voltage and variable wattage, here's an absolute truth that may help illustrate where the difference lies:
The quality of the vape is identical. You cannot tell from the taste, feel or any other aspect of your vaping experience whether a vv/vw device is set on watts, or set on volts.
Others have stated the reasons why many (including myself) prefer to set watts rather than volts, but none of those reasons create a difference in vape quality.
Yep your right. Really the difference is in how you adjust it. I went vw because there's no need to adjust wattage as your battery drains or when switching out tanks with different resistance. Vw you pretty much set it and forget it. I do switch wattage for some juices.