It’s not to increase battery life, it’s that when batteries degrade, the voltage can drop bellow spec when the current gets too high. So when the cpu hits its p

It’s not to increase battery life, it’s that when batteries degrade, the voltage can drop bellow spec when the current gets too high. So when the cpu hits its peak frequency, the battery voltage drops and the chip glitches causing a reset/reboot. Apple added an update that could detect these power failure reboots and cap the CPU frequency so your phone doesn’t crash all the time. Around the same time, a lot of Android phones like the nexus 6P were plagued with this issue where the phone would just randomly shut down.