"The iPhone version of Procreate, an excellent drawing app, is a case in point. It uses the Watch not as a canvas but as a tool palette. A nice thought, but once you’re wearing it, it’s amusingly obvious that you can’t use the Watch and iPhone at the same time. It’s anatomically impossible."
I've got no intention of buying a Watch but it occurs to me that by holding an iPhone in one hand and having the Watch rotated around my wrist 180 degrees (as I usually wear my watch) on the same arm I can make this very anatomically possible. You could quite easily go from tapping on the iPhone screen to moving your finger a couple of inches to the side for a tap on the tool palette and back to the iPhone screen.