If you spray meth you’re adding fuel…since meth is a fuel.
If it’s running too lean without meth you can add fuel by spraying meth, and that may add power by avoiding the stock ECU pulling some timing etc., but that’s not a proper solution. If it’s already rich, and timing is at max advance, and then you add meth with no other changes…it will slow you down.
I know you’re talking about the silly GM button nonsense and I am familiar with it. The problem is people stray from the parts that was designed for and then it’s anyone’s guess if the car will run OK or dangerously in that mode. I know it can revert if enough knock is sensed, but as I was saying, you know enough to know you should be actually tuning the car rather than playing with that.