on mechanicals, its because a battery only goes up to 4.2 volts on a full charge. so we wrap our coils sub ohm because a good vape is usually around 2-3 volts higher than the ohm of the coil. So 1ohm coil + 2-3 = 4 volts, yum! As the battery drains, the voltage to ohm ratio stays pretty good if your using low resistance on a mech mod. Where-as if you use standard res on a mech mod, bleh, the vape gets weak a quarter to halfway thru the batteries charge.