It all comes down to V = iR (Ohm's Law, Voltage = current x Resistance). Yes, I know, we actually get to use what we learned in high school in real life.
Depends on the Resistance(Unit: Ohm) of the coil in cartridge, the Voltage can be tuned to that "perfect" setting so that the right amount of i, current(Unit: Amp), goes through the coil.
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Science behind EV - Proneodox)
As per various voltage per various juices, I'm sure there is some effect, but our taste senses are not that sensitive. That's like asking, should I bake frozen pizza at 400F or 405F. I can't tell the difference even if there is one.
Some mods have power setting, so you need to understand P = iV (Power = current x Voltage). The unit for power is Watt.
Power is just another way to represent setting.
Some nominal setting are:
Voltage: 4-5 V
Resistance: 1-3.5 Ohm
current: 1.5-2 A
Power:4-8 Watt
Example:
If you set 4V with 2Ohm coil, i(current) = V / R = 4 / 2 = 2A.
Since P = iV = 2A x 4V, the Power is 8 Watt.
In English, higher the voltage, the hotter the coil get. Lower the coil resistance, again, the hotter the coil gets. The hotter the coil gets, it burns juice faster, means more vapor. One may say, why not make it super hot and done with it. For one, it can melt the plastics around tank/cartridge. Also, the high temperature of coil consumes battery faster. It also "burns" the fiber wick in the tank faster, and creates carbon around the coil.
Having said all that, it only matters to the people who wants that extra bit of control.
Vendors usually pre-set their device to match their tanks/cartridges for the best performance.
Happy vaping