Mainly concerned about Metal's affect on the GPU load, as well as any increase/decrease of battery life.
Metal is designed to be extremely efficient, the less work it has to do on both CPU/GPU, the more it will save battery. That's the point of focusing on reducing the overhead as much as possible.
You can have the most powerful GPU at 2000 watt in the world running a task for 1 sec and still have it be more power efficient compared to an average 300watt GPU running the same task at 1 minute, especially if both GPU idles at the same power requirement level. With overhead from OpenGL and CA or others, the first GPU could run 5-10 more seconds and already wasted more power than the average one.
The more idle both CPU/GPU are, the better. Metal is what supposed to do that. That's why Mavericks had battery life, they focused on
Timer Coalescing that collect most tasks in one operation to force the CPU into more idle power states.
