Just to expand on this a little with an example:
Every atomizer/clearomizer/cartomizer/etc. is built to a particular resistance (ohms) so:
2.8ohms x 4v = 11w
2.4ohms x 4.5v = 10.8w
1.8ohms x 6v = 10.8w
View attachment 269276
So, as you can see, regardless of the attached device's resistance, setting your 134 at a particular wattage will automagically adjust the voltage to match the resistance. So, regardless of the resistance rating of the attached device, you'll theoretically get the same kind of vape experience.
If you're device DIDN'T have variable wattage, every time you attached a new device, you'd have to adjust the voltage to taste.
In the end, it's all about saving you from having to make adjustments every time you attach something new to your 134.