I'm kinda disappointed that he didn't show the big smoke show that the vehicle exhibits during the procedure. That's the best part!
In the video, it said that the more Seafoam fuel treatment that you use, the better that it cleans... I wonder if an engine would run on straight Seafoam?
I'm not a fan of using such "snake oil", and certainly wouldn't want to wash any of the grime that has undoubtedly collected in the intake manifold through the combustion chamber. The potential is there for some of the gunk to collect on a piston or valve. Or possibly get caught in a catalytic converter, where it can cause far more problems than sitting in the intake.
While a dirty intake manifold is not ideal, it won't cause much harm either.
I just make frequent WOT pulls as a regular part of my "maintenance" program for keeping the inside of the engine clean.