“If you want to speed up your old iPhone, change the Region setting to France.”

Damage would be minimal if any at all for your avg user as pretty much everything comes with brownout protection these days. But you are not warned to repair the device when these events happen. Heck before the option to disable this became available everything was silent to the user. Personally I would call the IOS message a Notice over a Warning.

This option doesn’t prevent it from ever happening, but if the cpu restarts because of a brownout then the feature is enabled. Now the OS is more explicit the “warning” isn’t about damaging the device but about the device restarting on its own.

The argument about it holding your transit card and allows emergency services is a bit pointless. Stuff falls out of people wallets all the time, like cash and transit cards, people drain their battery on their phone all the time without considering “maybe I’ll have to use this later” even on healthy batteries.

I also wouldn't compare it to purposely buying a UPS that fails when encoding while compiling either, because the battery was fine (baring the 6s battery, but it was ok, just died quicker than would be expected) on the day of purchase and you would be able to “encode and compile” at the same time, what it would be like is buying a UPS that after a couple of years might not be able to always provide UPS backup if the power dipped while you were doing demanding work (In my case I could still listen to streaming music via wired headphones, just "only" when the battery was above 50% without restarts). The UPS warning you about such things, and the UPS auto telling the computer it’s connected to to slow down if it failed to prevent the connected PC from browning out during such workloads. (The phone re-enables the mode after brownouts, but tells you it has so you can turn it off again).

When my battery was failing in my old phone, the only time it would restart is when I was listening to streaming music via wired headphones, if I turned down the volume or used Bluetooth it was fine. (though YMMV) calls were fine, what finally pushed me to replace the battery wasn’t the restarts but the inability for fuel gauge to correctly report the remaining battery which could mean even with battery performance enabled I was left without access to my wallet stored on my phone because 10 mins ago the phone said 50% and now it’s reporting 3% (Due to the battery voltage curve no longer performing to the curve the fuel gauge was expecting with the curve dropping much quicker then a healthly battery would).

My point is we are often told risks, understand they exist and choose not to become overly cautious about said risks, most people choose not to carry battery packs on the off chance their can’t recharge our phones as expected and might need to use it, and those are on "healthy" batteries. (When I worked in a bar we would have a selection chargers and then battery banks because a rarely a shift would go by without someone asking where the power outlets were or if we had a charger for their phone, so it because a good customer service pratice to just have them on hand. The reason we shifted to power banks over charges was a) they basically became cheaper then chargers b) we had more seats then power outlets and they were in places customers would find annoying as they were placed out of sight so if you handed a customer a charger they would prob have to change seats to use it)

It just came across as a little scaremongering that’s all.