For documentary work, AF can be useful to eliminate focus hunting. The dual pixel AF has actually opened up a new world of opportunity to tell a story so differently than what we are currently used to.
Bringing in a larger crew just for focus pulling can alter a real life moment, but keep it minimalist to a one man band and you have a completely different way of telling a story.
And they really shouldn't call it "Dual Pixel AF" with the "AF" in there, because it's not the "auto" part of the technology I am interested in but rather the Servo part of it. It's the fact that you can drive focus precisely to where you need it to go without physically touching the lens then LOCK the focus.
From a storytelling perspective this offers a more polished way to tell a story while staying minimalist - an extra tool for me to use. Of course if I want the footage to feel a bit more organic then yes I would do 100% manual focus to get the focus hunting look in there.
I can't wait to test out this feature on the 7D Mark II to see how it performs.