So, I was talking to Lilian from Microsoft last week, and explaining how I didn't think I needed to buy a Surface Book device because the only difference between it and my Surface Pro 3 is that it has a Graphical Processor Unit (GPU) in it. I reckoned I that I had no need for GPU support because I don't play games or do graphical things. She reminded me that lots of programs, including Adobe Lightroom - which I use a lot - make heavy use of GPU hardware to speed things up.
I tested this theory over the weekend, running Lightroom on my HP Sprout, that has a reasonable GPU in it. Turns out she's right. The GPU makes raw decoding of images much, much, faster. So now I want a Surface Book. The big one. With the GPU.
Thanks for that Lilian.