Yes, I've read it, and it makes sense to me on the examples they talk about, the expression pedal and the wah, but what would you use the modifier curve for when the controller is an adsr?
Put simply, a modifier latches to a parameter in a block such as drive, mix, time etc. The modifier comes with settings regarding the shape of the curve, intensity, start and stop points ( the minimum and maximum you want to allow the parameter to move) you can also set a delay time to smooth the parameters change in position. Any parameter in a block with <-> can be assigned to its own modifier with its own entirely independent group of modifier settings. A Modifier needs to respond to an input control of some sort. It needs to be told when to move.
This is where the controller is plays a role. You can choose which controller is used at the top of each modifier menu. Controllers are Global across the preset but not global to the axe fx. Each preset has its own entirely separate controller settings.
The controller is the LFO, the envelope, the ADSR envelope, the pitch controlled envelope which moves the modifier. Each controller has its own settings.
You asked what purpose to have settings on both. A simple example you are creating an effect where you want two parallel filters to sweep a low cut shape and the same time but in an apprising fashion. You would attach the frequency of one filter to a modifier setting the controller to LFO 1, Setting the minimum to 0 and the maximum to 100 Then on the other filter you would set the frequency to a modifier setting the controller to LFO 1, Setting a minimum to 100 and the maximum to 0. Now when you change the speed, shape, depth of the LFO one controller, the behaviour of the frequency parameters in the two filters will correspond to LFO1 controller however the frequency of each with be in out of phase by 180 degrees. (When one is high the other is low) This is just a simple idea I just thought of obviously with something like this there are many many options.
I hope this is all clear for you