Of course you can use it in the function itself, just be cautious that you don't create cyclic references by doing something stupid :)
This parameter gets incredibly handy when you use one callback function for multiple controls:
const var buttons = []; for(i = 0; i < 128; i++) { buttons.push(Content.getComponent("button" + i); } inline function printMyIndex(component, value) { local index = buttons.indexOf(component); Console.print("You clicked button " + index); }; for(b in buttons) b.setControlCallback(printMyIndex);I've been using this paradigm in literally every project I am working on since it heavily reduces boilerplate code. Although it comes with a slight performance overhead because it needs to look up the index in the array, so if it's a time critical function, better code it manually...