At first glance, it might seem like a more complicated way of doing things, but it’s not. After a minor adjustment period, it will soon feel as natural as the default set up, maybe more so. It’s just so easy; thumb focus, finger capture. There are many things we do in everyday life which involves using the thumb and index finger simultaneously. And some of these things are actually good.
I find back button focus most useful for rapidly-changing scenes or quick-moving subjects commonly found in street and wildlife photography. You now have the ability to autofocus and recompose the scene without having the camera refocus again when you take an image. Just focus on your subject, make a slight change to the composition by moving the camera while your subject stays in focus, and then shoot. Pressing the shutter release only fires the camera. It doesn’t activate autofocus again.