Heat.
If you go back to my first post, I explain how the electricity through the coil causes friction which results in heating the coil. This is what vaporizes the
juice. A higher voltage will create more friction and thus, more heat. If the ohm rating for a coil is too low for the amount of electricity going through it, it will get too hot and, like a light bulb, burn out or pop.
This can be a safety issue and why you always want to make sure to not push too much current through a coil by setting the voltage too high and why you want a high enough resistance coil. A higher ohm coil will simply not allow the electricity through, and in that way, will produce less friction/heat. Basically, the higher resistance coil will simply not allow you to push too much current through it.
How hot you are heating the juices will affect taste. It's just like with food. A particular food will taste different when it is hot than when it is cold. Variable Voltage allows you to dial in the temperature of the
juice so that you can adjust the taste to your preference.
For instance, you might find that a particular
juice has a cocoa taste to it that gets really bitter at higher temperatures, but mellows out into a really nice creamy chocolate at lower temperatures. On the other hand, you might find a juice that has a vanilla flavour that simply disappears at lower temperatures and to really taste it, you have to dial up the volts.
It all comes down to getting the best taste out of your juice and your personal preferences.