It really doesn't. AMD has essentially the same perf/watt coming in a few months. ISA doesn't change anything nowadays because it all gets decoded into a per-CPU specific actual instruction set anyways.
This is not the difference between x86 and ARM -- it's the difference between Intel's team and Apple's (also AMD's). You don't see Qualcomm being competitive even though they also use ARM.
But in practice the whole decoder stage is basically a rounding error because cores got so big.
Basically, laptop chips that should be around 35% faster and use less power.