Variable Voltage is different from regulated and mech
mods. You can dial your voltage up, for more vapor, flavor, etc. Best to start low and adjust in small increments to taste or until it "feels right." (Or generally set it x2 your ohmage. 2.2ohms @ 4.1 volts, etc)
Variable Wattage gives you consistent power. You set it at whatever level you want, you leave it, you probably forget. It does not suffer from voltage drift - wherein your performance will drastically decrease as your battery drains its power. It will automatically adjust your voltage based on the ohm of your coil, and continue powering said coil at whatever level you leave it.
You don't absolutely NEED either. A coil, on a 3.7v eGO, at whatever ohms gives you the best vape (AKA your sweet spot) will certainly do the trick. That being said, the ability to dial up or dial down depending on what setup you're using, what
juice, etc... can be a very handy tool indeed.
It helps to mitigate a lot of problems that can occur by giving you a more tailor customed vape experience.
