“How dare they slow down my computer without telling me.”
The part you’ve missed, because you are NOT objective, is that Apple isn’t slowing down your computer in general, they are managing peaks of processor power that the battery cannot deliver. So it happens here and there, and only when you’re doing something CPU intensive that the aged battery can’t keep up with. If you want a feature to either turn this on or off, what it will mean if you turn it off is that your device will simply shut off when the battery can’t deliver enough power at a peak task time.
It isn’t possible to notify you in real time when this is happening and have you make that choice, it happens second to second. So you have two options. 1. The power curve-smoothing algorithm Apple has implemented, or 2. have an option to turn that off and instead of your phone slowing down during peak processor loads it just shuts off and guess what, you can’t do that particular task. That’s the problem Apple is trying to solve. Do you get it now? You either have your phone slow down during a peak load, or your phone just can’t do that particular task anymore because the battery is too degraded, and Apple can’t magically make batteries defy the laws of physics.
Then you’d be complaining that Apple is forcing you to get a new battery and why oh why can’t they just manage the power better and slow it down a bit at peak times so I don’t have to get a new battery.
You see, your phone isn’t being throttled all the time, this isn’t an either/or, on or off feature. If you give the user the choice to turn this off all that happens is your phone will shut off, seemingly randomly. What a great idea. Not.
Source : http://macdailynews.com/2017/12/20/apple-confirms-iphones-with-older-batteries-will-take-hits-in-performance/351