First, thanks to Epic for releasing such awesome tech at such an amazing price!
Obviously many people will want to develop for mobile platforms, however, many (such as myself) also want to develop from “mobile” platforms; a Macbook Air in my case but there are so many devices in the same category such as the Surface. On my Air the GPU performance is not terrible, it could be improved in the editor but when running the mobile previewer its actually pretty good, definitely fine for working on smaller scale games.
Unfortunately the CPU utilization and energy impact by extension seems a bit high from a cursory glance; I am simply using Activity Monitor and gauging battery performance while running the editor. Just sitting idle the Launcher is using about 4% CPU (thats a fair amount for such a simple process) and the Editor about 20-35%; and here is where it gets really weird…I am actually seeing more utilization when disabling “Realtime” in the viewport, the UE4Editor process jumps from ~20% to ~35% by disabling it which is pretty counter intuitive (and this is in an empty project). I can normally squeeze about 10-12 hours of battery time out of my Air (this is what they are known for), however, I think I would be lucky to see 1 hour given the CPU usage (not to mention it turns into a serious heat pump).
By contrast Unity uses ~1% CPU when idle in an empty project and allows for several hours of development on battery; it would be pretty amazing to see the same from UE4 and Im sure its only some slight optimizations away from that.