Tablet mode becomes possible because the battery and Intel Core processor are built into the screen half of the hybrid laptop, while that high-powered GPU is in the keyboard base. The idea is that you’d use the device in laptop mode, while connected to that graphics processor, when playing games, editing video, or typing. When you want to use it as a less-powerful clipboard-size tablet, it detaches from that GPU-packed base for lighter tasks. You can also re-attach the top half of the device display-side up for “draw mode,” which gives you access to that GPU and screen at the same time, albeit with a little more bulk.
That's one way to upend the new iPad Pro's graphics (or lack there of) capabilities. It's interesting to see the benchmarks coming out in November and December. Where's my Skylake enabled Retina MacBook Pro Apple?