So in other words, to make the trigger buttons to work. 0 on the trigger axis means its inactive, but for example to fire a weapon tell playmaker to detect 1 on the axis that the trigger is on, that should allow you to fire your weapon. untill you let go of the trigger and go back to 0 on the axis, and that will stop that fore action.
Almost. It never goes to 0 again. On the moment you start pressing the trigger, it will become the range -1 to 1. Just like a car's accelerator pedal.
As you press for the first time, and keep pressing further, it will start the linear progression of the axis, -1, -0.9, -0.8... until it reaches 1.
In your example, once you release the trigger after shooting your weapon, the trigger will decrease its axis from 1 to 0.9, 0.8... going through 0, until you fully release the trigger and it rests at -1.
You can link an action to any of these values if you want, for example, so the weapon only shoots a bit late but not so late, let's say, at 0.3. Or implement an acceleration action, like stretching a bow string to shoot an arrow for example, and depending of the stretching strength, a different damage is applied.
It's a very odd behavior, it should start at the range, but it starts at 0 instead, to never go to 0 again once pressed for the first time, unless you quit Unity or the Game.
You can use the Controller Tester asset from the asset store to observe this behavior, it's free.
If you think this is a bit complicated, wait until you have to work with the Steam Controller, which has it's triggers working as an axis and buttons at the SAME TIME. I hope the behavior is separated, and not hardcoded into a single bahavior.
My guess is that it will have a "click" virtual (or maybe physical) button at the end of each range, working as a real button, to separate itself from the accelerating range behavior. If my guess is somewhat correct, then it will not be so complicated at all.