ARM offers, in the best case and ideal situation, a vastly more power efficient package that offers pretty good and modern performance. Peak performance with x86 is much higher, but at a very disproportionate cost in power. Something like 2x performance for 20x the power. (Measurements are not exact, direct comparison is impossible and there are many chips of each architecture)

So for any device with a battery, ARM is generally superior. That's why basically all mobile phones are ARM and have been for 10+ years.

The move for windows for arm is largely about the future of laptops and not so much desktop, however, as performance increases for ARM chips and complexity In design improves, there is a good argument for ARM becoming a rough standard even for desktop, over the next 10 years.

There are similar architectures to ARM that are even more efficient, and open source (cheaper for manufacturers) such as RISC-V, that offer even more promise in the very long term, but they are much much much earlier in development. The first RISC-V chips that are actually for users are just now hitting the market.