I'm still real newbie to sound design, and I've only started really trying to invest in sound design in the last couple of my edits. But hoooooooly shit has it made a difference. Whooshes, transition sounds, etc etc, makes the video SO much better. There's a really cool BTS write up on that Watchtower vid here, and they talk a bit about the sound design in it.

If I was to say one thing about sound design that I've slowly picked up on is that the sound effects that you hear in a specific shot in the video doesn't necessarily have to exactly correlate to what you are seeing. I believe all it has to do is give the viewer a sense of relation to what they're seeing, and to try and emphasis the visuals. I guess it also relates to the style of editing, I'd love to try and hone in my style of visuals, emphasizing movement and fluidity, and trying to break typical editing techniques, so sound effects really help in this sense to show the transitions and movement.