I recently worked on a few projects that have involved the Errol Morris' Interrotron set up. It is a nice set up that gives the viewer the feeling that the interviewe is talking directly to them.
My DOP/Filmmaker friend and old school buddy Jay Ferguson has done this set up several times but throughout the years he has managed to make it more and more compact. Something that is actually hard to do since it involves to the core a lot of gear but he has been able to build a run and gun version (2 briefcases, no lighting). Idealy, the camera set up involves 2 teleprompters that are rigged together so that the interviewe can see the interviewer. This technique was the brainchild of the pionier of Documentary filmmaking Errol Morris renders interesting results.
This is what I discovered on the recent shoot that involved Proffessional Golfers. They are pretty media savvy bunch and they have there life story pretty boiled down to a "canned anecdote". If you put a talented interviewer at work with the Interrotron the result is that in about 10-15 minutes they "let go" of these stiff responses and basically talked to you like your at a dinner party (that is the best way I can put it).
Another advantage is that if the subject isn't use to the lights, camera and crew then this focusses them on the face of the interviewer. We had 2 other cameras (side shot and a roving cameraman) and the interviewe never did acknowledge there repositioning, reframing and moving around them; which traditionally is distracting.
I can see why Errol uses this technique and how he got one of the most media savvy public figures (see FOG of War) to open up to him. The visual result is great but the amount of great moments captured is the real motivation to use this style of Doc filmmaking.