It's a _theoretically_ excellent one but only under the proper conditions
the low-power-e cores on intel CPUs are not inside of the main core complex, they're in the I/O die; if they're the only cores active, and the power management is configured correctly, the _entire main CPU body_ can be effectively shut off.
Theoretically, as long as LPE-cores are sufficient (mainly idling, maybe just a text editor open, or video playback through the GPU without CPU involvement etc), it reduces CPU power consumption by a pretty decent amount - but CPU power consumption isn't really a _huge_ factor anymore, so it ends up being like...10-20% difference in battery life IIRC?
I _think_ some of the video-playback-only battery life tests are some of the best results _because_ the CPU is basically off for 4k video playback now?
