While I do believe the arm chip in Macs will bring an improvement in efficiency, I have doubts it will be as significant as you and many people are predicting based on the iPads efficiency. ipadOS is a completely different beast from macOS so it’s not straightforward extrapolation. To get that kind of efficiency I think Apple would have to make macOS more ipadOS-like. I think the main reason for Macs going arm is for Apple’s benefit, but I do think that independence from Intel could allow Apple to innovate in this space, and benefits could spill over to us consumers, depending on what they’re able to do. We’ll see soon!Generally ARM is more power efficient. So either you could build a MBA with same power and perhaps double the battery life. Or you could in the same thermal capacity (think MBP) provide more power.
In the longer term Apple can provide more dedicated silicon integrated with the CPU as they today do with SSD controllers. This could result in very good performance for specialized use cases.